Hi again,
you cannot do this directly. You can, however, create a standard ROOT histogram from a PDF:
https://root.cern.ch/doc/master/classRooAbsReal.html#a6659d2c301e5cd65b83ee8c9422c2553
The options for the generation of the histogram are also listed in the documentation I linked above.
When you have the TH1x, subtraction of the histograms should be easy.