To diagnose the issue further we need the following information.
Input file(s) - unless you can reproduce with any file
Generated output file(s) - if you were able to generate one
Code you used to generate the output.
First though, you should try the latest version
Latest official: https://www.pdftron.com/pdfnet/downloads.html
Release channel: http://www.pdftron.com/nightly/?p=stable/ Latest official builds, and Release channel, are ready for production usage, however the developer channel builds do not get the same amount of testing and can be in a state of change.