An expanding, portable envelope for use in transporting papers compartmentalized into organized sections is formed of a base sheet and a divider sheet. The two sheets are secured by a pair of transverse lines of sealing across the bottom of the envelope. A pair of divider panels is thereby created from a single divider sheet. Moreover, the bottoms of the pockets created between the divider sheets and the front and rear panels formed from the base sheet are closed, so that papers cannot slip down underneath the divider panels. The base sheet defines side panels that extend from one of the front and rear panels, and are heat sealed to the other. Bottom attachment tongues formed as extensions from the side panels are directed inwardly toward each other at the bottom of the envelope and are also permanently attached to the divider sheet so as to close and reinforce the bottom corners of the expanding envelope.