Many chess authors release "sampler" packs. You can find legitimate free PDFs on:
: Includes verbal explanations that address why certain logical but incorrect moves fail New In Chess No Clue Tests 600 Modern Chess Puzzles Pdf Free Download
Many positions are taken from games played in the last few years, ensuring you haven't memorized the solutions from other books. Many chess authors release "sampler" packs
You can often find a multi-page preview containing several puzzles on the Gambit Books PDF repository . 600 Modern Chess Puzzles Pdf Free Download