Program file that contains source code written in the Pascal programming language; can be edited with a Pascal development program or a basic text editor.
PAS files can be compiled into executable programs using a Pascal compiler such as Turbo Pascal.
Program(s) that open pas files
Mac: FreePascal; Edit with a text editor Windows: Turbo Pascal; Borland Delphi; Edit with a text editor
Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/pas