Rule 8, Section 1. Article 3 of the rule explains that a pass is completed when he secures control of the ball with his hands or arms,
touches the ground with both feet or any other body part (other than his hands), and
maintains control long enough to allow him to perform “any act common to the game,” which includes having the ball long enough to “pitch it, pass it,
advance with it, or
avoid or ward off an opponent.”
Jerry Markbreit
When a catch is made by a receiver who comes down with both feet on the ground, the "football move" would be:
stretching for a first down, diving out-of-bounds or
running with the ball. If the "football move" is accomplished, and the receiver is then hit and the ball comes out, it is ruled a catch and fumble, instead of an incomplete forward pass.
http://www.chicagotribune.com/sport...41027jerrymarkbreitsanswers-story.html#page=1