A document managing method for a printing device is provided. The document managing method includes the following steps. Firstly, a printing mechanism prints a document with plural papers, and transfers the plural papers to a paper collection platform. Then, a management module manages the plural papers from two lateral sides of the plural papers. Then, a paper ejection module ejects a first portion of the plural papers at a first speed, and then ejects a second portion of the plural papers at a second speed. Consequently, the plural papers are exited from the paper collection platform. Then, the management module is separated from the two lateral sides of the plural papers, so that the plural papers fall down to a supporting tray. The first speed is faster than the second speed.