Adobe Pagemaker has a dedicated PDF export function and supposedly also InDesign (or at least some of its versions) could also work with the *.pm6 documents from PageMaker 6. Without any of these programs program, it will be very hard to convert PM6 files as PDF documents, if not impossible.
Convert Adobe PageMaker document to Adobe Portable document format.
We have found 3 software records in our database eligible for .pm6 to .pdf file format conversion.
Microsoft Windows software - convert pm6 to pdf on Windows
Professional desktop document publishing software from Adobe
Convert from pm6 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 pm6 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.
One of the first desktop publishing programs on market
Apple macOS / Mac OS X software - convert pm6 to pdf on OS X
Mac version od Adobe's popular document designing and publishing software