String handling issue with Free Pascal

[SilverWarior]

And for the memory issue, this is exactly my problem why I can't store these in a file or something like that.

Go and read my post again. I made you a caclulation in order to show how much memory or HDD space you would require in order to save all posible string variations if you have string 12 character long and there can be 23 posible characters. Even if you go and save that to your hard drive I doubt you have computer with almost 20000 terabytes of hard drive space.

and Pascal doesn't like the idea that the string's length might also be changed in the process, and I'm still searching for a counter.

Pascal doesen't have any problems when you change string size. Simply use the function I proposed.

A recursive approach would also work, because then with a character length of 12, only 12 strings would be in the memory at a single time, but unfortunately I couldn't come up with a working recursive code for this problem.

How did you come up to that? Why do you think you would need 12 strings in your memory?
The number of strings in your memory could only be affected by the number of concurent processes you intent touse (multithreading).
For recursive approach you only need one string stored in the memory at any time. The only thing is that this string gets updated every time before MD5 has is generated from it.