Start with the filename
A file type describes how information is stored in a file. You can often recognize it by the extension: the letters after the final dot in a filename, such as .pdf in meeting-notes.pdf. Your device uses the file type to suggest an app that can open it. Knowing a few common extensions makes it easier to choose how to save a file, understand an attachment, or ask for a version you can use.
An extension is a useful clue, not a guarantee. A file can have the wrong name, and changing its extension does not convert its contents. If a file will not open, check whether you have an app that supports its format. You can also ask the sender to export it in a more widely supported format. Some devices hide extensions by default; their file information or properties view can usually show the full name and type.
Documents: choose between editing and sharing
Document formats differ mainly in how much formatting and editing they preserve. A .txt file contains plain text. It is easy to open on many devices, but it does not keep features such as headings, tables, or images. A .docx file is commonly used for editable word-processing documents. An .odt file serves a similar purpose and is used by some office applications. If you are collaborating, agree on an editable format that everyone can open before work begins.
A .pdf is often useful when you want someone to read, print, or complete a document without its layout changing unexpectedly. A PDF is not necessarily easy to edit, though, and some PDFs are scans made of page images rather than selectable text. If a recipient needs to revise your work, send an editable copy as well. For important shared documents, give files descriptive names and check the exported version yourself: confirm that pages, links, and any form fields behave as intended.
Images: balance size, quality, and purpose
A .jpg or .jpeg is a common choice for photographs. It can keep photo files relatively small, but repeated saving or heavy compression may reduce visible quality. A .png is useful for screenshots, diagrams, and graphics with sharp text or transparent areas; it may be larger than a JPEG photograph. A .webp can store photos or graphics efficiently, although it is worth checking that the people receiving it can open it with their software.
A .gif may contain a short animation, but it is not usually the best choice for a detailed photograph. A .svg stores vector graphics, which can stay sharp when resized; it is often used for simple illustrations or logos. When sharing an image, consider more than the extension. Use a clear filename, keep a copy of the original before resizing, and add a text description where your platform allows it so people who cannot see the image still understand its purpose.
Audio: consider playback and file size
Audio files can differ greatly in size and compatibility. An .mp3 is a familiar option for spoken recordings and music, and it is supported by many devices. A .wav often stores less-compressed audio and can be much larger, making it useful when someone needs to edit a recording. An .m4a is another common format, especially for recordings made or shared through certain apps. An .ogg file may work well in supported players, but it is less familiar to some recipients.
For everyday sharing, start with a format the recipient can play rather than assuming the smallest file is best. If an audio attachment is too large, check whether your recording app offers an export option at a smaller size. Keep an original copy before converting it, since conversion may lower quality. For a spoken message, a brief written summary or transcript can also help people who cannot listen to the recording.
Archives: several files in one package
An archive bundles files and folders into one package, often reducing their total size. The most familiar example is .zip. Other extensions include .7z and .tar.gz; a recipient may need a compatible extraction app to open them. An archive is handy for sending a folder of related documents while keeping its structure. Extracting it creates accessible copies of the files inside; it does not necessarily open those files for you.
Before sharing an archive, give it a meaningful name and check that it contains only the intended files. Before opening one you receive, consider whether you expected it and trust its sender. Be particularly careful with unexpected attachments that ask you to run a program or enable special features. If a recipient struggles with an archive, offer the individual files instead. The most useful file type is the one that lets the other person complete their task without unnecessary steps.
