Abstract: An apparatus for forming a pliable package having a flat bottom is disclosed. The apparatus includes a hollow guide form (16). The guide form, in a preferred embodiment, has a rectangular cross-section. Also provided are means (2) for forming pliable sealable material (12) which is received from a continuous roll, around guide form (16) to form a continuous seamed packaging preform (30). Members (32), (34) are also provided for advancing the continuous packaging preform (3) such that a seamed preform (58) extends below bottom (20) of guide-form (16). A pair of opposing and movable tucking jaws (60) and (62) are located close to the bottom end (20) of guide-form (16). Each of the tucking jaws includes a pair of pointed extension members (68) and (70), and (72) and (74) respectively separated a selected distance, for contacting and partially collapsing preform (58) to form a tuck in the preform (58) when tucking jaws (60) and ( 62) are moved toward each other.