Document (Microsoft Publisher)
PUB is a file extension for a document file format used in Microsoft Publisher, a desktop publishing program that is a component of the Office product suite. Through Publisher, users can create, edit, publish, manage and share content.
PUB files are a proprietary format, which is not widely supported. Outside of Microsoft applications, Adobe PageMaker and Corel Draw X4 can open PUB files. However, the PUB files cannot be edited in those applications.
MIME type: application/x-mspublisher
Learn more about PUB files:
See the Microsoft Publisher website.
See questions and answers about Microsoft Office on ITKnowledge.com.
Wikipedia has an entry about Microsoft Publisher.