I found an interesting facts related to the XPS document on Sharepoint, you can read the issue here. He is using Microsoft XPS Viewer to open and digitally signs an XPS document but he found the following facts:
- XPS documents are not signed while the signing process has been done before.
- The XPS document is locked on a server.
- All document properties (metadata) are set to its default values.
He assumed that this was because Microsoft XPS viewer uses XPS document location for its temporary files, while updating the document it creates at least two temporary files in Sharepoint library, thus resulting in problems such as above.
But when he used the XPS Annotator, he did not experience such problems like when he used the Microsoft XPS Viewer. So can be concluded that currently the XPS Annotator is more Sharepoint friendly.