Hi,
Thank you for the details!
I downloaded one of the PDF documents for local testing, I hope you don’t mind. I’m afraid that none of the parsers is capable of extracting the document contents. The most advanced one (Smalot Parser) was able to get around 100 words from the files, but the rest is only gibberish. I tried a few different ones locally as well, also converting the files, looking at the datastreams, but no luck. I’m afraid there is no standalone PHP parser currently able to extract these documents. These might require a more advanced server side library, which is unfortunately not possible to integrate with the plugin.