The base.dcl and acad.dcl files are included with AutoCAD and are distributed in the User Support folder. To see the path to the User Support folder, from the Tools menu, click Options. On the Files tab, the path to the User Support folder is the first path displayed under Support File Search Path.
The base.dcl file shows the DCL definitions for the basic, predefined tiles and tile types. It also contains definitions for commonly used prototypes. The PDB feature does not allow you to redefine the predefined tiles. The acad.dcl file contains the standard definitions of all the dialog boxes used by AutoCAD.