This document (....) probably uses a compression technique which is not supported by the free parser shipped with FPDI

This is a request to add some advice to the documentation. I hit an error with the PDF file being produced when using a PDF template that has a compatiblility level greater than PDF 1.4. I got the error "This document (....) probably uses a compression technique which is not supported by the free parser shipped with FPDI"

See the documentation here: https://www.setasign.com/support/faq/fpdi/error-document-compression-tec...

I also found this answer here: https://stackoverflow.com/questions/12154190/fpdf-error-this-document-te...

So, to overcome this I used ghostscript (loaded by default on most linux systems, but you can probably get it for Windows) as follows:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dNOPAUSE -dQUIET -dBATCH -sOutputFile="new.pdf" "old.pdf"