If you are looking for structured PDFs or books with endgame puzzles, these are the gold standards in the chess community: 100 Endgames You Must Know
: Often called the "multiplication tables" of chess; everything else builds from these. Rook Endgames : The most common endgame type. Focus on the Lucena Position (winning) and the Philidor Position (drawing). The 3P Rule chess endgame puzzles pdf
: Despite the title, it scales in complexity. It includes dedicated chapters on winning a piece in three moves and coordinating three different pieces to force a win. 100 Endgames You Must Know Workbook (Sample) If you are looking for structured PDFs or