A filename extension is the ending after the final dot. It helps the operating system choose which application should open the file.
Documents and data
Common document formats include .docx for word-processing documents, .xlsx for spreadsheets, .pptx for presentations, .txt for plain text, and .pdf for fixed-layout documents intended to look similar across devices.
A PDF is useful for sharing a finished copy, while the original editable file should be kept when future changes are likely.
Images, audio, and video
.jpg is common for photographs; .png supports sharp graphics and transparency; .svg stores scalable vector graphics. Audio formats include .mp3 and .wav. Video formats include .mp4 and .mov.
Opening a format depends on available software and the codecs it supports.
Compressed and executable files
.zip files package one or more items into a smaller or more convenient bundle. Extract the contents before editing them unless the application specifically supports working inside the archive.
Executable and script formats such as .exe, .msi, .app, .bat, and .js can run instructions. Treat unexpected executable attachments as unsafe.
Extensions can be misleading
A renamed extension does not truly convert a file. Changing photo.jpg to photo.pdf does not create a PDF. Use an application's Export or Save As feature to convert formats.
Enable filename extensions when practical so a file named invoice.pdf.exe cannot masquerade as an ordinary document.
Quick skill check
- Recognize common document and image extensions
- Keep editable originals when needed
- Extract ZIP files before ordinary use
- Do not run unexpected executable files
- Use Export or Save As for real conversion