XFA Documents Cannot be combined.
When trying to combine documents with one or more PDF documents that have interactive form fields, you get an error that XFA documents cannot be combined.
During the conversion process, one or more documents will have the error XFA Documents cannot be combined.
This is due to the fact that PDF Converter Professional and PowerPDF are not currently compatible with PDF forms created using Adobe XML Forms Architecture (FXA) data. These forms are created by Adobe Live Designer and can only be combined in that program. If you try to combine these forms in Adobe Acrobat you will get an error message there too.
An acceptable work around is to print the documents in question to ScanSoft PDF create and save them. They now can be combined without error.
If the client would like the forms fields to be active after conversion, take the converted document, open it and go to Forms / Forms Typer. Re-save the document.
This will now allow you to open the combined document and fill in the form fields.