Currently, the only detachment gives your Psychic weapons (auto-wounds on a 6 to hit) and allows you to re-roll a single Hit or Wound roll per unit per phase. If your PDF says "Brotherhood of Psykers" or "Tides of the Warp," you are looking at an old edition.
For tournament play and the most accurate rules, the physical Codex combined with the Warhammer 40,000 App is the gold standard. However, for theory-crafting and list building, many players utilize army builder applications like BattleScribe or New Recruit , which pull from the Codex data to help you build lists without needing to manually flip through pages. grey knights 40k codex pdf
As of the latest balance dataslate, the Grey Knights do not have a full 10th Edition codex yet. Instead, Games Workshop (GW) released a free Index Grey Knights PDF when 10th Edition launched. This index contains all the datasheets, army rules (Teleport Assault), and Detachment rules (The Prescribed Host). Currently, the only detachment gives your Psychic weapons
This gives you the speed of a PDF with the accuracy of live updates. However, for theory-crafting and list building, many players