If you’ve never come across Microsoft Publisher before then here’s a neat explanation from wikipedia.
“Microsoft Publisher is an entry-level desktop publishing application from Microsoft, differing from Microsoft Word in that the emphasis is placed on page layout and design rather than text composition and proofing.”
It’s actually quite a neat application for newbies to desktop publishing like me, but it’s a difficult tool to handle if you receive *.pub files (the format used by MS Publisher) and are asked to translate them. And I do see requests from translators from time to time asking how they can handle them. The file itself is a binary format and even with Office 2016 (which includes Publisher if you have the Professional version) the only export formats of PDF, XPS and HTML are not importable. So very tricky indeed if you need to be able to provide your client with a translated version of the pub format.