Old Adobe PageMaker does support export of its own formats to RTF and perhaps also to plain text. In case of Rich Text documents, you can import them to Microsoft Word, or similar word processor and save as plain text. Only the text will be converted however, special effects from PageMaker will not.
Convert Adobe PageMaker 5 document to Simple text file.
We have found 2 software records in our database eligible for .pm5 to .txt file format conversion.
Microsoft Windows software - convert pm5 to txt on Windows
One of the first desktop publishing programs on market
Convert from pm5 file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned pm5 to txt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert pm5 to txt on OS X
Mac version of once popular publishing program