Are you trying to combine files but:

- Receive error: "Unable to open selected document"?

The Combine Files feature is available in Corporate Edition 3 and 4 as well as Office Edition 4.

Note: This error occurs when one or more of the PDF documents being combined were created using the scanner software that came with you scanner.

To resolve this issue, you will need to re-create the PDF documents so they are all in the same format.

Please click the link below to visit our Learning Center for Office Edition 4. Please review the articles: Create from Applications or Create from Scanner to produce PDF documents in a standardized format.
Learning Center

If this does not resolve your issue, please submit a support ticket detailing your experience.