Volo's and Xanathar's are compendium additions, so yes you can drag and drop them. From Volo's marketplace page : Bestiary provides game statistics and lore for nearly one hundred monsters suitable for any D&D campaign. Gain access to rules and story for dozens of monsters new to fifth edition Dungeons & Dragons, such as the froghemoth, the neogi, and the vargouille. Included in the Roll20 version of Volo’s Guide to Monsters: Brand new Compendium entries will unlock upon purchase, fully integrated with the D&D 5th Edition Compendium. Over 130 statted Tokens featuring original artwork from Dungeons & Dragons. Find these in the Compendium tab of the Roll20 tabletop and drag & drop into your game to add terrifying new monsters to your adventure! Delve into the belly of the beasts with all 7 monster lair Battle Maps from the book, set up in the included module. The module is advanced feature-enabled, with Dynamic Lighting on all 7 Maps. Designed for use with the Roll20 Official 5E OGL Character Sheet