Microsoft Publisher is able to export its own documents (.pub files) directly to PDF document format (.pdf). This is the most convenient way how to perform pub to pdf conversion, but not everyone may have access to the program.
But perhaps you can find and use other tools, such as LibreOffice with PubOOo extension, that will give you the option to Publisher files and export them to Adobe PDF.
Articles and other information relating to pub into pdf conversion:
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