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What is a .pub file?

A .pub file is a Microsoft Publisher (version 2.0). This one is a specialist format without an obvious everyday home. Confusingly, this extension has been used by 12 different formats over the years — they're all listed below.

This extension has been used by more than one format

12 different formats have claimed .pub over the years, so two files with the same extension aren't necessarily the same kind of thing.

How to open a .pub file

The program that created it is by far the most reliable way to open it.
On Windows, use a hex viewer or the free TrID tool to identify what the file really is.
On Mac or Linux, running `file yourfile` in the terminal identifies most formats instantly.

The registry records this extension against Microsoft Publisher, Microsoft Publisher, Microsoft Publisher and others, so software from that family is the most likely match.

How to convert a .pub file

Identify the file first, then look for an export or Save As option in whatever program can read it.

MIME type

When a .pub file travels over the web, servers label it with this MIME type:

application/x-mspublisher

What's a MIME type?

The technical record

For archivists, developers and the merely curious: these are the PRONOM registry entries for .pub.