Old Adobe Pagemaker can export its own documents to a PDF format. It doesn't seem there is any other program that supports Pagemaker formats, so it is probably the one and only choice for this conversion.
Convert Adobe PageMaker document to Adobe Portable document format.
We have found 2 software records in our database eligible for .pmx to .pdf file format conversion.
Microsoft Windows software - convert pmx to pdf on Windows
One of the first desktop publishing programs on market
Convert from pmx 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 pmx to pdf. 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 pmx to pdf on OS X
Mac version of once popular publishing program