You are understanding is correct, It is currently no possible to read-write data card variables to PDF files But however
If you are Converting to PDF's using tasks, You could copy the SolidWorks file's variable values to the PDF's data card.
I don't really have a need to do this myself but you can probably do it 'on the cheap' with a combination of Dispatch using a parameter file and a cmd executing a pdf metadata editing program like the one below.
If I were trying to do if I would try making a parameter file that saves all of the information about the pdf files that you want to write (location of files, metadata to set and values for that metadata) and then write a cmd batch file that uses the information in that parameter file to write the metadata to the file.
If that all works then you have a good idea of what to get your friendly programmer to do - an ADD-IN would be your best final solution.
Thanks for the input, Tim. Since I've never written any cmd executables, I ended up doing this through Excel VBA. Took awhile to execute, but did the job.