A desktop publishing application from Microsoft that focuses on page layout and graphic design.
Yep - you can make Microsoft Publisher (MSPub) the default application for .pub files, provided Microsoft Publisher is installed on the computer.
The easiest way is to right-click any .pub file in File Explorer and select Open with > Choose another app. Select Microsoft Publisher from the list, check Always use this app to open .pub files, and click OK.
You can also do it through Settings > Apps > Default apps. Search for .pub, select the current default application, and choose Microsoft Publisher. After that, double-clicking a .pub file should automatically open it in Publisher.
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hth
Marcin