The only way how you would ever convert PTX templates to PDF format would be to use the old Adobe PageMaker, as no other program is probably capable of this conversion.
Convert PageMaker template file to Adobe Portable document format.
We have found 2 software records in our database eligible for .ptx to .pdf file format conversion.
Microsoft Windows software - convert ptx to pdf on Windows
One of the first desktop publishing programs on market
Convert from ptx 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 ptx 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 ptx to pdf on OS X
Mac version of once popular publishing program