The standard ways to pick up an object is with the 'take' command (see 'help take'). However, when an object is too heavy or large, use the 'lift' command to pick it up.
Corpses can also be 'lifted', instead of dragged (with the 'grapple' command). Lifting is considered a non-violent command and you are able to jump across roofs with corpses or throw them off edges. Note that you may not be able to lift certain objects because of your stats. Objects may be too heavy or you may be too weak. While lifting an item, you might also drop it because the weight is unbearable for you to hold that long. So, if you find that an item disappeared, it's most likely you dropped it while moving through rooms.
