The PDF.TCTwoDViewer recommended for 64bit environments is a TcVis viewer. In order to view a PDF, TcVis Embedded Viewer needs to be installed and have permission for both "opening/viewing" and "Content Copying". Another option is to use Adobe Reader but it will take a bit more configuration to work correctly (see 7429849, 7636778 on GTAC).
Don't forget to run %TC_ROOT%\portal\registry\genregxml.bat.
NX 11.0.1.mp01 | SW 2016 | TcUA 11.2.3