I have thousands of games & also tactics problems in .pgn files but can't imagine how a book could be in pgn format. Can you provide any sources where I could examine one ?
Chess books in PGN format

90+ Percent of Books from Everyman are available in PGN. Go to their eBooks page. Go to the Everyman Site itself, not Amazon. You go to Amazon and it will be Kindle format.

Thanks for the answers but I'm still not clear on the format.
I went to everymanchess.com. They publish eBooks. I'm not aware of any standard ebook format that's equivalent to pgn. According to the specs a pgn file is a text file listing games or problems in three parts (1) tag pairs (2) movetext & (3) comments.
That polgar pgn file provided is simply a list of problems, not a textbook.

Thanks for the answers but I'm still not clear on the format.
I went to everymanchess.com. They publish eBooks. I'm not aware of any standard ebook format that's equivalent to pgn. According to the specs a pgn file is a text file listing games or problems in three parts (1) tag pairs (2) movetext & (3) comments.
That polgar pgn file provided is simply a list of problems, not a textbook.
When one says pgn form of textbook they mean the games and not the entire book and when it comes to book of tactics and puzzles that is all you may need.
Chess books in PGN format is a real deal, especially those of tactics. What all books are you aware of which is in PGN format?