When trying to use ReadDoc for externally generated PDF files I get the following error :
I think you mean VPE files, not PDF files. VPE files are the native file format of VPE, which allows to store documents in a transportable and highly compressed format.
201 Document file has the wrong (higher) version and can not be opened / read
As the error message tells, you are trying to open a VPE document file, which has been created with a higher edition. You have for example installed the Standard Edition, but the document was created with the Professional Edition. Higher editions can always open documents that have been created with lower editions. But because higher editions do offer additional types of graphical objects (for example RTF - Rich Text Format, or 2-dimensional (2D) Barcodes) a lower edition cannot open documents, which have been created by a higher edition.
Solution: Install a higher edition of the VPE trial-version.
To create a PDF file from a VPE file, create a new VPE document in memory by calling OpenDoc(). Read the VPE file using ReadDoc() and write the PDF file using WriteDoc("some file.pdf"). By specifying ".pdf" as file suffix, VPE will create automatically a PDF file. You may also modify several options for compression, encryption, font embedding and font subsetting before calling WriteDoc() - please see the help files / manuals. The next version of VPE will also support PDF/A.