Parsing a file with C# code

My requirement is to re-factor the code from old architecture to new architecture. I do not want to change any business logic. I just have code from old architecture that too in a notepad files.

TODO: 1. I need to find out the dependent methods from different .cs files and paste them into my new architecture.

Ex: There are two class A with method A1, A2, A3...etc and class B with method b1, B2, B3...etc. Now A1 call B2 which call C2 which in turns calls Common class. In my new architecture I want A class with A1 method, B with B2 and C with C2 only as .cs files. I will be getting the dll's for common method.

Is there any possibility of writing a parser with C# as theoretically it seems possible to me.

Also I cant use any of 3rd party API for this.

Please provide some suggestions, or any helpful link. I can use dll's provided by Microsoft within VS.