Help finding a fast permutation / combination algorithm in C #

I used the algorithm found here in CodeProject , which worked well. I want the length of each permutation to be the same as the number of characters that I used to generate the permutations (for example, "code" will give "code", "coed", "cdoe", etc.)

I want to do this in order to find an algorithm that will give me all permutations / combinations regardless of length (for example, "code" will give "c", "co", "cod", "code", "coe", "coed" and etc.)

Am I using the correct terminology? Any help would be greatly appreciated. Thanks