PAK
A PAK file is the data format used by the original Lynx ROM and several ports (the extension .pak is used by the DOS port) to store a single level. It can only contain level data conforming to the Lynx Ruleset.
In the DOS port, each level is stored as a separate .PAK file. In the Spectrum and Amstrad CPC ports, each level file contains up to eight PAK-format levels.
C4 can convert levels between DAT format and PAK format.
Unlike DAT, the PAK format uses a compression system to reduce level size. Programs that manipulate PAK files must expand them before editing them, and compress them when saving.