Are there any other restrictions or limits on the PDX program?

Due to technical limitations, at present the PDX system can only process priority documents that contain about 1,000 pages or fewer. For very large documents, applicants should file the paper certified copy of the foreign applications rather than filing a request to retrieve electronic priority applications.

Further, priorities claimed in international applications filed under the Patent Cooperation Treaty are excluded from participation. This includes retrieving or transmitting any international application as a priority document as well as requesting retrieval of any priority document for placement within an international application. Additionally, design applications are also excluded from participation.

USPTO FAQ - Questions and Answers (31Jul2009)