How to open any file

1490 extensions, taken from the FileExtensions field that publishers declare in their installer manifests. The number next to each one is how many indexed programs register to open it.

Changing or showing a file extension in Windows is a different question, and the short answer is that renaming one never converts the file.

Written for the formats people actually get stuck on, with the step-by-step for Windows and macOS and the specific reason each one refuses to open.

• .msiWindows Installer packageA .msi file is a database of everything an installer needs to do, which Windows itself reads and executes. Double-clicking one installs it. Unlike a setup .exe there is no installer program inside: Windows Installer is doing the work, which is why MSI packages uninstall, repair and deploy the same way across every program that uses one.
• .pdfPortable Document FormatEvery operating system and browser opens PDFs natively. If yours will not open, it is almost always password-protected, and there are two different passwords with very different consequences.
• .msgOutlook message fileA .msg file is a single email saved by Microsoft Outlook in its own proprietary format. With Outlook installed it opens on a double-click. Without it, you need a viewer, because unlike .eml it is not readable text.
• .docxWord documentA .docx file is a Word document. LibreOffice, ONLYOFFICE and Google Docs all open it for free. If Word says it is corrupt, the file is a ZIP internally and can often be repaired.
• .msixMSIX app packageA .msix is Microsoft’s modern app package. Double-clicking one hands it to App Installer, which unpacks it into a managed container rather than running a setup program. Every MSIX has to carry a valid digital signature or Windows refuses it, which is the main practical difference from a plain .exe installer.
• .mdMarkdown documentA .md file is plain text with light formatting marks. Any text editor opens it, but to see it rendered with real headings and links you want a Markdown editor such as Obsidian or VS Code.
• .rarRAR archiveA .rar file is a compressed archive. On Windows 11 (23H2 or newer) and modern macOS you can open it without installing anything; on Windows 10 and earlier you need an archiver such as 7-Zip.
• .exeWindows executableAn .exe is a Windows program. macOS cannot run one, and no download makes it possible directly. Your options are a compatibility layer such as Wine or CrossOver, or a Windows virtual machine.
• .htmlHTML documentAn .html file is a web page. Double-click it and your browser opens it. To see or change the code behind it, open the same file in a text editor instead.
• .cabWindows Cabinet archiveDouble-clicking a .cab opens it like a folder, which is why installing one confuses people: opening and installing are different things here. What installs it depends on the contents. A Windows package goes in with DISM, a driver with pnputil, and a cabinet that is simply an archive only needs extracting.
• .dllDynamic Link LibraryA .dll file is compiled code that programs load, not something you open. If a program says a DLL is missing, install the runtime it belongs to. Never download an individual DLL from a website.
• .tarTape archiveA .tar file bundles files together without compressing them. macOS and Linux open it with a double-click or one command; on Windows use 7-Zip, and expect to unpack twice if it ends in .tar.gz.
• .pkgmacOS installer packageOn a Mac, a .pkg is an installer: double-click it and Installer.app walks through the steps. On Windows it will not install at all, because the contents are macOS software, though an archiver can still open it to look inside. The extension is also used by PlayStation and BSD systems for unrelated formats.
• .xlsxExcel workbookAn .xlsx file is an Excel workbook. LibreOffice Calc, ONLYOFFICE and Google Sheets all open it free. Like .docx it is a ZIP inside, so a corrupt one can often be recovered.
• .psdPhotoshop documentA .psd file is a layered Photoshop document. GIMP and Photopea open it for free with layers intact, and Photopea runs in a browser with nothing to install.
• .apkAndroid packageAn .apk file is an Android app installer. It only installs on Android, where you must first allow installation from unknown sources. On a computer you can inspect it, because an APK is a ZIP archive.
• .zipZIP archiveEvery version of Windows and macOS opens .zip files natively. Double-click it. If that fails, the archive is either corrupt, password-protected, or larger than the old 4 GB format limit.
• .jarJava archiveA .jar file is a Java program packaged as an archive. To run it you need a Java runtime installed; to look inside it, rename it to .zip and extract it, because a JAR is a ZIP file.
• .epubElectronic publicationAn .epub file is an ebook. Calibre opens it on any desktop, and SumatraPDF is a lighter option on Windows. If it refuses to open, the book is DRM-protected and tied to the store you bought it from.
• .vcfvCard contact fileA .vcf file holds one or more contacts as plain text. Double-clicking imports it into your address book; opening it in a text editor shows the raw details immediately.
• .aiAdobe Illustrator artworkAn .ai file is Illustrator vector artwork. Inkscape opens and edits it for free. Many .ai files are also valid PDFs, so renaming a copy to .pdf often lets any PDF reader display it.
• .mboxMailbox archiveAn .mbox file is an entire mailbox stored as one plain-text file. Thunderbird imports it, and because it is text you can open it in an editor to confirm what is inside.
• .datGeneric data fileThere is no single .dat format. The extension just means "data", so the answer depends entirely on which program made it. If it arrived as an email attachment called winmail.dat, it is an Outlook formatting wrapper and needs a TNEF reader.
• .jsonJSON data fileA .json file is plain text. Any text editor or web browser opens it. If it appears as one unreadable line, it is minified and you need an editor that reformats it.
• .heicHigh Efficiency Image ContainerA .heic file is the photo format iPhones use by default. macOS opens it natively. Windows needs the free HEIF Image Extensions, and historically also a paid HEVC codec, which is why so many people convert instead.
• .pagesApple Pages documentA .pages file is an Apple Pages document with no official Windows support. The fastest route is iCloud.com, which is free and needs no Mac; the offline trick is to rename the file to .zip and extract the PDF preview inside.
• .svgScalable Vector GraphicsAn .svg file is a vector image written in XML. Every browser displays it, so dragging it onto a browser window works instantly. To edit it, use Inkscape; to read the code, any text editor.
• .taxTurboTax return fileA .tax file is a TurboTax return, and the extension carries the year: .tax2023, .tax2024 and so on. Only the desktop TurboTax for that exact year opens it. There is no free viewer and no converter.
• .dmpMemory dumpA .dmp file is a snapshot of memory written when Windows or a program crashed. It is not readable in a text editor. You analyse it with WinDbg, and the useful part is usually one line naming the driver that failed.
• .dwgAutoCAD drawingA .dwg file is an AutoCAD drawing. Autodesk publishes a free official viewer, and LibreCAD or the free web viewer will open one without a licence. Editing it properly still needs real CAD software.
• .stepSTEP 3D modelA .step file is a 3D CAD model in an open standard format. FreeCAD opens and edits it for free, and on Windows 10 or 11 the built-in 3D Viewer displays one on a double-click.
• .csvComma-separated valuesA .csv file is a plain-text table. Any spreadsheet opens it, but double-clicking it in Excel silently corrupts leading zeros, long numbers and dates. Import it instead of opening it.
• .emlEmail message fileAn .eml file is a single saved email in plain MIME text. Thunderbird and Outlook open it directly, and in a pinch you can rename it to .txt and read it in any editor.
• .xmlXML documentAn .xml file is plain text. Drag it into any browser to see it as a collapsible tree, or open it in a code editor to work with it.
• .epsEncapsulated PostScriptAn .eps file is a vector graphic, usually a logo or print artwork. Inkscape opens and edits it for free; IrfanView and XnView MP will display it if you only need to look.
• .rbxlRoblox Studio place fileAn .rbxl file is a Roblox place, and only Roblox Studio opens it. Studio runs on Windows and macOS only, so on a Chromebook you cannot open one. That is a platform limit, not something you are doing wrong.
• .kmlKeyhole Markup LanguageA .kml file holds map data: points, paths and shapes with coordinates. Google Earth opens it, Google My Maps imports it in a browser, and because it is XML you can read it in any text editor.
• .gzGzip archiveA .gz file is a single compressed file. macOS and Linux decompress it with a double-click or one command; on Windows use 7-Zip. If it is a .tar.gz there is a second layer underneath.
• .pakGame package archiveA .pak file is a game archive, and there is no single .pak format. What opens it depends entirely on which engine built it, so the first step is identifying the game rather than looking for a universal tool.
• .binBinary fileA .bin file is raw binary data with no single meaning. Most commonly it is a disc image that pairs with a .cue file, in which case mount it or open it with an archiver.
• .kmzZipped Keyhole MarkupA .kmz file is a zipped .kml plus the images it uses. Google Earth opens it directly, and renaming a copy to .zip lets any archiver show you what is inside.
• .dcmDICOM medical imageA .dcm file is a medical scan in DICOM format, the standard for MRI, CT and X-ray images. A free viewer such as MicroDicom on Windows or Horos on macOS opens it. Ordinary image viewers will not.
• .pstOutlook data fileA .pst file is an entire Outlook mailbox in one file. Outlook opens it directly. Without Outlook you need a conversion tool, because unlike .mbox it is a proprietary binary database.
• .rpmsgRights-protected messageAn .rpmsg file is an encrypted email protected by Microsoft rights management. Only the account it was addressed to can open it, and only through Outlook or the Microsoft encryption portal. There is no viewer and no workaround.
• .icsiCalendar fileAn .ics file is a calendar event or a whole calendar, stored as plain text. Double-clicking adds it to your calendar app, and opening it in a text editor shows the date, time and location directly.
• .dbDatabase fileA .db file is a database, and most of the time it is SQLite. DB Browser for SQLite opens those for free. Check the first bytes first: a real SQLite file begins with the text "SQLite format 3".
• .7z7-Zip archiveA .7z file is a compressed archive made by 7-Zip. Windows 11 23H2 and newer open it natively; on anything older, install 7-Zip or NanaZip.
• .isoISO disc imageAn .iso file is a complete disc image. Windows 8 and later mount it with a right-click, and macOS mounts it on double-click. No software is needed just to see what is inside.
• .torrentBitTorrent metainfo fileA .torrent file contains no content of its own. It is a small index of what to download and where to find peers, and it needs a BitTorrent client such as qBittorrent or Transmission.
• .tifTagged Image File FormatA .tif or .tiff file is a high-quality image. Windows Photos and macOS Preview both open it. If it fails, the file is probably a multi-page scan or uses a compression variant that basic viewers do not read.
• .pptxPowerPoint presentationA .pptx file is a PowerPoint presentation. LibreOffice Impress, ONLYOFFICE and Google Slides all open it free. Like .docx it is a ZIP inside, so a damaged one can often be salvaged.
• .stpSTEP 3D modelA .stp file is exactly the same as a .step file: an ISO 10303 CAD model. FreeCAD opens and edits it free, and the Windows 3D Viewer displays it without installing anything.
• .pngPortable Network GraphicsEvery operating system, browser and image viewer opens PNG files. If yours will not open, the file is damaged, incomplete, or is not actually a PNG despite its name.
• .phpPHP source fileA .php file is source code, so any text editor opens it. If your browser downloaded one instead of showing a page, the server failed to execute it, which is a server problem rather than yours.
• .jsxJSX source fileA .jsx file is plain text and any editor opens it. Be aware the extension covers two unrelated things: React component source, and Adobe ExtendScript automation scripts.
• .vttWebVTT subtitlesA .vtt file is a subtitle track stored as plain text. Any text editor opens it to read, and VLC loads it alongside a video to display the subtitles properly.
• .savSaved game fileA .sav file is a saved game, and the format belongs to whichever game wrote it. There is no universal viewer. What you can do depends entirely on the game or emulator involved.
• .cbzComic book archiveA .cbz file is a ZIP full of images, one per page. A comic reader such as YACReader or Calibre opens it properly, and renaming a copy to .zip lets any archiver extract the pages.
• .rbxmRoblox model fileAn .rbxm file is a Roblox model, a single object or group rather than a whole place. Roblox Studio opens it, and you insert it into an existing place rather than opening it on its own.
• .movQuickTime movieA .mov file is Apple's QuickTime video container. VLC plays it on any platform. On Windows it often fails not because of the container but because of the codec inside, usually ProRes.
• .jpgJPEG imageEvery device and browser opens JPG files. If yours will not, the file is truncated, is not really a JPEG, or Windows Photos is misbehaving and another viewer will open it fine.
• .rtfRich Text FormatAn .rtf file is a formatted document that almost every word processor opens. On Windows this got harder recently: Microsoft removed WordPad, so use LibreOffice, Word or the web.
• .vcardvCard contact fileA .vcard file is the same as a .vcf: one or more contacts stored as plain text. Double-clicking imports it into your address book, and a text editor shows the details directly.
• .mppMicrosoft Project planAn .mpp file is a Microsoft Project plan. Project is a separate paid product, not part of Office. ProjectLibre opens most .mpp files for free and is the practical answer.
• .mkvMatroska videoAn .mkv file is a video container. VLC plays it on any platform with nothing else installed. If it opens but shows no picture or no sound, the container is fine and a codec inside it is not supported.
• .harHTTP ArchiveA .har file is a recording of browser network traffic, stored as JSON. Open it in your browser devtools Network tab, or in any text editor. Treat it as sensitive: it usually contains session cookies.
• .pubMicrosoft Publisher documentA .pub file is a Microsoft Publisher document. Microsoft is retiring Publisher in October 2026, so this is a format on its way out. LibreOffice Draw opens many .pub files, imperfectly but usefully.
• .swfShockwave FlashA .swf file is a Flash animation or game. Flash Player was discontinued in 2020 and browsers removed it entirely. Ruffle, a free open-source emulator, is now the way to play one safely.
• .jpegJPEG imageA .jpeg file is identical to a .jpg. Every device opens it. If it will not open, the file is damaged or is not really a JPEG, because the software is never the problem here.
• .dxfDrawing Exchange FormatA .dxf file is a CAD drawing in Autodesk's openly documented interchange format. LibreCAD and FreeCAD open it free, and unlike DWG the specification is public, so support is far better.
• .pyPython scriptA .py file is a Python script, which is plain text. Any editor opens it. To actually run it you need Python installed, and then "python script.py" from a terminal.
• .tmpTemporary fileA .tmp file is scratch data a program left behind, and the contents depend entirely on which program made it. Most are safe to delete. The exception worth knowing is a Word or Excel temp file that may hold unsaved work.
• .stlStereolithography meshAn .stl file is a 3D model made of triangles, the standard for 3D printing. Windows 10 and 11 display one in the built-in 3D Viewer, and Blender or FreeCAD open it for editing.
• .aviAudio Video InterleaveAn .avi file is an old Microsoft video container. VLC plays essentially all of them. Failures are almost always the codec inside rather than the container itself.
• .ipynbJupyter notebookAn .ipynb file is a Jupyter notebook: code, text and saved output in one JSON file. VS Code opens and runs notebooks natively, and Google Colab does it in a browser with nothing installed.
• .htmHTML documentAn .htm file is exactly the same as .html: a web page. Double-click it and your browser opens it. To see the code, open the same file in a text editor.
• .mobiMobipocket ebookA .mobi file is an older Kindle ebook format. Calibre opens and converts it. Note that Amazon stopped accepting MOBI through Send to Kindle in 2022, so converting to EPUB is now the practical move.
• .cbrComic book RAR archiveA .cbr file is a RAR archive full of page images. A comic reader such as YACReader opens it, and renaming a copy to .rar lets 7-Zip extract the pages.
• .vobDVD Video ObjectA .vob file is a chunk of DVD video from the VIDEO_TS folder. VLC plays one directly, and to watch the whole disc properly you open the folder rather than an individual file.
• .xpsXML Paper SpecificationAn .xps file is Microsoft's fixed-layout document format, its answer to PDF. Windows removed the XPS Viewer by default, so the practical route now is converting to PDF or installing the optional feature back.
• .txtPlain text fileA .txt file opens in any text editor on any device. If yours will not open, the file is either enormous, which crashes Notepad, or it uses an encoding your editor is reading wrongly.
• .figFigma design fileA .fig file is a Figma design. You open it by importing it into Figma in a browser, which is free with an account. There is no offline viewer, and MATLAB figures also use .fig, which is a different thing entirely.
• .tiffTagged Image File FormatA .tiff file is the same as a .tif: a high-quality image, often a multi-page scan. Windows Photos and macOS Preview open both, and IrfanView handles the multi-page case properly.
• .gpxGPS Exchange FormatA .gpx file holds a GPS track, route or set of waypoints as XML. Any text editor shows the coordinates, and free tools plot it on a map without installing anything.
• .dmgApple disk imageA .dmg file is a macOS disk image. On a Mac you double-click it and it mounts. On Windows there is nothing useful to do with one, because the software inside is Mac-only anyway.
• .acsmAdobe Content Server MessageAn .acsm file is not your ebook. It is a small download token that Adobe Digital Editions exchanges for the actual book. Install Adobe Digital Editions, authorise it, then open the .acsm.
• .azw3Kindle Format 8 ebookAn .azw3 file is a Kindle ebook. Calibre opens it if it has no DRM. If it came from your Amazon library it is protected, and the Kindle app on that account is the only way to read it.
• .rawCamera raw imageA raw file is unprocessed sensor data from a camera, and every manufacturer uses its own extension: .cr2 and .cr3 for Canon, .nef for Nikon, .arw for Sony. Darktable and RawTherapee open all of them for free.
• .ddsDirectDraw Surface textureA .dds file is a game texture in a format designed for graphics cards. Paint.NET with the DDS plugin, GIMP or XnView MP all open one. Ordinary image viewers will not.
• .inddAdobe InDesign documentAn .indd file is an Adobe InDesign layout. Only InDesign opens it properly, and only a version equal to or newer than the one that created it. There is no free alternative that reads the format.
• .dwfDesign Web FormatA .dwf file is a read-only published version of a CAD drawing, meant for sharing rather than editing. Autodesk's free Design Review opens it, and it is deliberately not the editable source.
• .srtSubRip subtitlesAn .srt file is a subtitle track in plain text. Any editor opens it to read, and putting it next to your video with the same name makes VLC load it automatically.