Documents
PDF, DOCX, FB2, EPUB, DJVU
File formats: what opens them and how to convert
Every file on your computer or smartphone has a format — it is defined by the extension (.pdf, .heic, .iso, .json) and tells the system which program to use to open the file. When the right app is missing, you get the familiar error "Windows can't open this file", or Android simply ignores the attachment.
Updated: 22 June 2026LoadFile editorial team6 min read
This guide solves the problem: for every popular format we have gathered proven ways to open, view and convert the file — for free and without risk to your data.
Below, formats are grouped by category. Choose the one you need and jump to the detailed "how to open .X" guide.
Contents
Images
HEIC, WEBP, SVG, RAW, EPS
Video and audio
MKV, MOV, FLAC, M4A
Archives
RAR, 7Z, TAR.GZ
Code and data
JSON, XML, CSV, YAML
Disks and images
ISO, DMG, MDF, IMG
Documents
Text documents, spreadsheets and presentations are the most common reason to consult this guide. Formats like .pdf and .docx open almost everywhere, but e-books (.fb2, .epub, .djvu) and legacy office extensions (.doc, .rtf, old .pages) often leave users stuck.
The main rule: PDF is universal and opens right in the browser, whereas editable formats are best opened with their "native" app — otherwise the layout breaks. For a one-off task an online viewer will do; for regular work, install the free LibreOffice suite.
If a file won't open, in 90% of cases the cause is a wrong extension or a corrupted download.
How to open popular document formats:
How to open PDF
Opens right in the browser, the universal document format.
How to open DOCX and DOC
Word, LibreOffice and online editors without losing layout.
How to open FB2
E-books: apps and online readers.
How to open EPUB
The e-book standard for all devices.
How to open DJVU
Scans of books and documents: viewers and converters.
Tip
Don't know a file's extension? Turn on the display of extensions in Windows Explorer — we show you how.
Images
Ordinary .jpg and .png cause no trouble — any system opens them. Difficulties start with modern and professional formats: .heic from iPhones, .webp from the web, .raw/.cr2/.nef from DSLR cameras, and vector .svg, .eps, .ai.
HEIC is the leader in the number of questions: photos from an iPhone don't open on Windows and Android "out of the box", even though their quality is higher than JPEG at a smaller size. This is solved either by installing a codec or by converting to JPG.
How to open popular image formats:
How to open HEIC
iPhone photos on Windows and Android: codecs and conversion.
How to open WEBP
Images from the web: browsers, viewers, converters.
How to open SVG
Vector graphics: browser and graphics editors.
How to open RAW (CR2, NEF, ARW)
DSLR camera shots: viewing and processing.
How to open EPS
A vector format for print and design.
Video and audio
Media files are finicky because of codecs: the extension (.mkv, .mov, .avi, .flac) is just a container, and inside there may be a codec your player doesn't understand. Hence the classic: video plays without sound, or sound without picture.
There is one universal solution — the free VLC player, which plays almost everything. The standard Windows player doesn't support many of these formats.
How to open popular media formats:
How to open MKV
A video container: VLC and other players.
How to open MOV
Apple video: players on Windows and Android.
How to open FLAC
Lossless audio: players that support the format.
How to open M4A
An audio container: playback and conversion.
The universal VLC player
The free VLC player plays almost all video and audio formats without installing codecs.
Archives
Archives compress and package files. Windows itself unpacks .zip, but .rar, .7z, .tar.gz require a separate program — most often the free 7-Zip. A common problem: the archive asks for a password or throws an "archive is corrupted" error — usually this is an incompletely downloaded file.
How to open popular archives:
How to open RAR
A popular archive: 7-Zip and other free extractors.
How to open 7Z
The 7-Zip format with a high compression ratio.
How to open TAR.GZ
An archive from the Linux world: unpacking on Windows and Mac.
Code and data
Data and source-code formats (.json, .xml, .csv, .yaml, .sql, .log) open as plain text, but become "readable" only in the right editor with syntax highlighting. The free VS Code editor or online viewers with auto-formatting solve the task in seconds.
How to open popular code and data formats:
How to open JSON
Data in text form: editors and online viewers.
How to open XML
Structured data: highlighting and formatting.
How to open CSV
Spreadsheets: Excel, LibreOffice and text editors.
How to open YAML
Configs: editors with syntax highlighting.
Disks and images
Disk images are a "snapshot" of an entire medium in a single file: .iso, .img, .dmg, .mdf/.mds, .nrg. The most common is .iso. You can open an image in two ways: mount it as a virtual drive or burn it to a flash drive/disc. Windows 10 and 11 can mount .iso with built-in tools.
How to open popular disk images:
How to open and mount ISO
A disk image: mounting and burning to media.
How to open DMG
A macOS disk image: opening on Windows.
How to open MDF and MDS
Alcohol/Daemon Tools images: mounting.
How to open IMG
A disk image: mounting and burning.
Frequently asked questions
How do I find out a file's format if the extension isn't shown?
Turn on showing extensions: in Windows Explorer open the "View" tab → tick "File name extensions". After that the format will appear at the end of each name (for example, photo.heic).
Why won't a file open even though the program is installed?
Three common causes: the file didn't finish downloading (corrupted), its extension was swapped (a different format inside), or the program version is out of date. Try opening the file with another app or downloading it again.
Which single program opens most formats?
There is no universal "everything" solution, but three free apps cover 80% of tasks: VLC (video and audio), 7-Zip (archives) and LibreOffice (documents and spreadsheets). For images and code — VS Code and system viewers.
Is it safe to use online converters?
For non-sensitive files — yes. But documents with personal or commercial data are better converted locally, on your own computer. Read how to do it safely in the file security section.
Read also
Tools
Tools for working with files
A navigator across converters, archivers, viewers and developer utilities: which one you need when and what is safer — online or desktop.
Tools
10 free online file converters
Need to convert a document, image or video to another format right in the browser? We've gathered proven services — no install and no registration.
Security
File security: checking and protection
A complete guide: how to scan downloads for viruses, encrypt data, transfer files safely and make backups. Practice and proven tools.
In brief
A file's format is defined by its extension — it hints which program to open it with. Most tasks are solved by five free tools: VLC, 7-Zip, LibreOffice, VS Code and system viewers. If a file won't open — check whether it is corrupted and whether its extension is correct. Choose your category above and move on to the step-by-step guide for a specific format.
Didn't find your format?
See the full catalog of proven free programs and online services for working with files.
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