The anchor may not be a pawn, but the capturing piece may be a pawn. Converted pieces may be of any rank except king.
All opposing pieces between the capturing piece and the anchor are converted to the color and army of the capturing piece and anchor.
Example: White is in check, but has no piece that can take the checking piece. White can, however, take another piece that puts the checking piece between two white pieces, and thus convert it and save the king.