Until now very little was known about the format. It is not officially documented. Nevertheless I have recently determined sufficient information about the latest format to read and write PVK files in a form that is acceptable to various tools that use PVK files. This information was not derived using anything other that freely documented structures and the examination of some sample files. This description refers to the PVK format used by Xenroll version 5.102.1680.101 and signcode version 5.101.1663.1 it may well be incomplete or inaccurate if other versions are used.
All integers are in little endian format.
The file consists of three sections. The precise meaning of these is unknown but here is my interpretation. The meaning of reserved is unknown. It was always zero in the files I tested. It is 1 for a key exchange key and 2 for a signature key.