Understand your files

Practical answers to a few everyday file mysteries.

How to identify an unknown file type

Find out what a file is when it has no extension, the wrong extension, or refuses to open. Learn what file signatures can—and cannot—tell you.

What does a file extension mismatch mean?

Understand why a file’s extension can disagree with its contents, when renaming helps, and why changing an extension does not convert a file.