File section dividers for an expandable filing case are formed with expansive partitions having pocket panels extending from their lower edges and folded up and secured to the partitions. The pocket panels are formed with at least one linear pocket delineation seal parallel to the opposing side edges of the pocket panels. The pocket delineation seal divides the panel into a plurality of pockets which will have different sizes, depending upon the placement of the pocket delineation seal or plurality of seals. Preferably, pocket apron flaps are provided at the upper edges of the pocket panels to facilitate insertion and removal of documents and other objects into the pockets of the file section dividers. The file section dividers find their greatest utility when employed in a collapsible, portable document storage device having side panels formed into pleated accordion folds. Side edge marginal strips at the lateral, outboard extremities of the file section divider partitions are secured to corresponding surfaces in each of the pleated folds of the side panels.