The community will undergo maintenance on October 16th at 10:00 PM PDT and will be unavailable for up to one hour.
How to create a Report(Query Builder) or Webject to list all documents types in Windchill.
Take a look at this document with lots of report ready to use.
I think you should use this report to start.
QML report to count the number of documents by different document types
https://support.ptc.com/appserver/cs/view/solution.jsp?source=subscription&n=CS216381