Let’s get Familiar with Delphi Files
Before starting writing something in the code window, it’ll be great to get some familiarity with Delphi file types. If you create a delphi project you’ll see files with different extensions. Here are their explanations.
.PAS – These are the main files in which you’ll write most of your code. The extension comes from the first three letters of the name of Delphi Ancestor "Pascal".
.DFM – These are the files in which your GUI based information is saved i.e; any form that you’ll create will have 2 files, 1 .dfm and other one .pas. the .dfm file will contain the information about controls, where those has been placed, their link and the .pas file will contain the code, you’ll wrote.
.DCU – Some sort of compiler specific files for debugging etc. Will be created each time you compile your project.