Most programs offer two methods of installation lets call them:
Express Install - This method installs the program into C:\ProgramFiles
Custom Install - This method lets you choose where it goes.
If you choose the later, you might for example install Adobe Photosho[p into D:\Adobe\Photoshop and much of the files will be installed there. But two other things will happen.
1. Adobe will still install what it calls "Common Files" into C:\ProgramFiles. These are various files that are common to multiple applications from Adobe and when you install any other programs from Adobe, they want those files to be where the install program expects them to be.
2. Windows has a registry which you might think of as switches or pathways...