(You'd use it if the destination is already somehow specified. "rauflegen" is more idiomatic, but "drauf-" also works. "her-" does NOT, despite what textbooks might imply.)
2.
to add on top, to put on top of
(In the context of adding an extra sum or compensation on top of a base - "drauflegen" is the more idiomatic choice. Usually in combination with "müssen".)