Not sure what you mean. you can choose a custom install location during the install and the download location has something to do with your browser....
In order to "move" from C:\ to D:\ you will have to first uninstall and then reinstall in the D:\ drive.
No application should be dragged from one drive to another as there is information stored in a Registry of where several files are located (their paths or routes) in the computer drives/disks.
In order to select an alternate install location for Adobe Reader you need to use the full installer; download it from http://get.adobe.com/reader/enterprise/
Flash Player installs into the Windows folder; you cannot change that.
I tried the method of uninstall and reinstall the Adobe Reader. I was on the lookout for the custom installation but there was no such option during the download /installation stage. It automatically stored everything in the C:\ without asking me for the option.
It looks like the only possible way is to try the one suggested by Pat Willener. Yes, it worked as there was an option to change to D: drive in the process.
If Pat Willener could also suggest similar links for Adobe Download Manager and Adobe Flash Player, that would be even better.
I don't remember if the Adobe Download Assistant has an option to select the install / download locations; you will have to try this by yourself.
Flash Player will install in your Windows folder; if it's on the C: drive, then there it will go. But it's just a browser add-on; not really big software.
You cannot choose where to install Flash Player, because browser plug-ins must go to fixed folders.
Also... when you install any software, information is added to the WIndows Installer database, which is on C. Often this is a LOT of information. Really, you need to get a bigger C, you can only make very small savings by choosing software install locations.