File Extension Library (A–Z)

A simple directory of common file types — what they are, what they’re used for, and what to do if one won’t open.

What this library is

Files usually end with an extension (the letters after the dot), like .pdf or .jpg. That extension is a quick hint about the file’s format and which apps can open it. But extensions are not perfect: some formats are shared by multiple programs, some files are mislabeled, and some downloads get renamed by websites or email clients.

This library is built to answer the real-world questions people run into: What is this file? What program opens it? Is it safe? How do I convert it? Each page focuses on one extension and gives practical guidance (not filler): common uses, where you typically see the format, and what to try when a file won’t open.

If you’re not sure what you have, start by checking the extension and then compare it to the file’s context (where it came from, what you expected to download, and whether it opens in a trusted viewer). When needed, conversion is usually the quickest fix — for example, turning a document into PDF, or an image into PNG/JPG. This library also links related formats so you can quickly jump between similar file types.

File Extension Library (A–Z)

What this library is

Library index

Numbers

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z