A file won't open: the most common reasons and how to fix them
Double-click, and nothing happens, or an error says the file is damaged or not supported. Surprisingly often the file itself is fine and only the program is missing something. A few checks show which case you have.
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1. The extension does not match the content
The ending of a file name is only a label. A PNG renamed to .jpg, a WebP image saved as .png by a browser, or a download page stored as .pdf all carry the wrong label. Some programs refuse such files, others open them without complaint.
The first bytes of a file reveal its real type. A PDF starts with the characters %PDF, a PNG with PNG after one special byte, a ZIP archive and every DOCX or XLSX file with PK. If a supposed PDF begins with <!DOCTYPE html>, you downloaded a web page, often a login or error page, instead of the document. The file check reads these bytes for you and names the real type, without uploading the file.
2. The download or copy is incomplete
An interrupted download, a full USB stick or a sync conflict can leave a truncated file. Compare the size with the original if you can. A video that stops halfway, a ZIP archive that reports errors or a PDF with missing last pages are typical signs.
Cloud folders can also contain placeholders. Files marked as online-only exist only as a small stub until they are downloaded, and copying that stub elsewhere produces a file that cannot be opened.
3. The format is fine, the decoder is missing
Videos from newer phones often use HEVC, also called H.265. Many players and browsers on Windows cannot decode it without an extra extension. Professional formats such as ProRes are rarely supported outside editing software. Converting the video to a widely supported format solves this, as long as your browser can read the source.
iPhone photos in HEIC are the image equivalent. Where they do not open, convert HEIC to JPG in a browser that can display them.
4. The file is protected
Password-protected PDFs, encrypted Office documents and encrypted ZIP archives cannot be opened without the password, and no tool should promise otherwise. Ask the sender for the password or for an unprotected copy.
Some PDFs open but refuse printing or copying. That is a permission setting of the document, not damage.
A quick checklist
Work through these checks in order; the first ones take seconds.
- Compare the file size with what you expect. A few kilobytes for a video means something went wrong.
- Download or copy the file again from the original source.
- Try a second program or a current browser.
- Check whether the real type matches the extension.
- For videos and photos from phones, convert them to a widely supported format.
- For protected files, ask the sender for the password or an unprotected version.