Doc1 Designer allows to import external documents. On importing a PDF, following error is observed:
This could be caused by the fact that the Version of the PDF being imported is greater than 1.3.
For more info, refer limitation under "External Document" is Designer User guide.
ResolutionUPDATED: July 27, 2017
Ghostscript can be used to lower the version of PDF. Refer How to downgrade PDF version to import into Doc1 Designer