FormFiller uses the PHP class FPDI to read pages from existing PDF documents. By default FPDI can "only" handle PDF documents up to PDF version 1.4. Beginning with PDF version 1.5 there were new compression features introduced which involve internal structure changes how a PDF document can be created. Google Drive / Google Docs generates PDF documents version 1.5 which are not supported by the free parser shipped with FPDI.
FormFiller uses the PHP class FPDI to read pages from existing PDF documents. By default FPDI can "only" handle PDF documents up to PDF version 1.4. Beginning with PDF version 1.5 there were new compression features introduced which involve internal structure changes how a PDF document can be created. Google Drive / Google Docs generates PDF documents version 1.5 which are not supported by the free parser shipped with FPDI.