File extensions: formats, categories and uses

An extension guides an app, but it does not convert the file

The part after the last dot helps an operating system suggest an application. .pdf, .png, and .mp4 are familiar shortcuts, yet a filename does not change the bytes stored in a file. Renaming photo.png to photo.jpg does not make it JPEG; conversion requires software that can export the content in the needed format.

Use the table to find a category, format name, and common use. It does not replace the requirements of the destination: a platform may accept PNG and reject TIFF, or require its own size limit, color profile, and dimensions.

Extension, format, and MIME type are different checks

An extension is a filename signal; a format is the actual content structure; a MIME type identifies data in web transfers and responses. They often align, but can differ after a rename, mistake, or server configuration. For an important upload, integration, or received file, also check the type detected by the operating system or receiving service. The IANA media types registry is a useful source for registered MIME types.

Choose a format with the destination in mind

• For reading or printing, check whether the recipient needs PDF or an editable document.
• For web images, confirm accepted formats, size, and transparency before exporting.
• For archives, make sure ZIP, 7Z, or another option can be opened by the recipient.
• For data, do not treat CSV, JSON, and XLSX as interchangeable: they preserve fields, formulas, and structure differently.

An unusual name or double extension deserves attention

An unknown extension does not prove danger, and a familiar one does not prove safety. Be cautious with names that hide the real ending, such as report.pdf.exe, unexpected attachments, and files that ask to enable macros. When the source is uncertain, confirm the sender and use the available checks before opening it.

Are .jpg and .jpeg the same?

Yes. Both spellings normally refer to JPEG; the difference comes from older systems that limited extensions to three characters.