Create an high compatibility PDF

Our Finance dept has to create a large PDF several times a year. This PDF typically would have 300+ pages that combine several documents such as project schedules, contracts, agreements, etc. As part of our Hyland OnBase workflow, this PDF gets converted to TIFF but it could not. OnBase uses PDF technology from Datalogics and when I used Datalogics online PDF checker, the PDF failed to process. https://www.datalogics.com/products/pdf-tools/pdf-checker/

We have tried flatten the PDF (print to PDF from Chrome), optimized from Adobe but the PDF continued to fail to convert to TiFF. We finally used Peernet TiFF Image Printer 3rd-party software to do the TiFF conversion and inserted the the single TiFF file into the workflow to proceed. Any suggestion on what Adobe PDF options we can use to make the PDF more compatible? and hopefully allow it to be converted to TIFF with no problem. Sorry, I can't attach the confidential PDF here. Hope you understand.