Yeah I just posted a similar question (in For Beginners) but not specific to this one program.
https://www.chess.com/forum/view/for-beginners/better-computer-resources-how-to-use-which-ones
Looking forward to advice 
Struggling with Chess Position Trainer
Sort:
Mar 17, 2019
0
#3
I used CPT and changed to Chessable. Chessable, as CPT, uses spaced repetition, but there you can purchase books, which was not possible in CPT. You should really have a look, perhaps you can take one of the free books (like Basic Endgames) to test it.
Hello Everyone,
I recently purchased Chess Position Trainer and exploring it. I am having some issues with it.
While trying to import opening pgn files it shows following message:
" You are about to import 330170 positions.A single topic/opening should rarely cover more than 10000 positions (in many cases less than 3000 is enough).Only import PGN files from an opening or repertoire ebook. Do not import a collection of games where no selection of candidate moves has been done yet.Otherwise you will have to manually update thousands of positions to define for all positions where your side has to move, which candidate move is your first choice."
I downloaded some PGN files for various openings from internet but they all are having this issue. I tried reducing the number of moves to import to 20 also but still the number of positions were too high.
So my question is, where can I get such opening ebooks that will work for Chess Position Trainer. I want to build a very solid and deep repertoire (25+ moves).
Kindly help me out with this.
PS: Please don't judge me by my games. I mostly play on my computer and chess24.
regards
Shashank