Text file manipulation

Hi All,
I have the following text file which can contain thousands of lines each day.
Example

25,516582,B-003,C:\CAF\25-00000103\25-00000001.PDF

I need the script to read the first number 25 and the second number 516582 from each line (Thee numbers will be different on each line) and make the line look like below the only consistent thing about each line are the comma's.

25,516582,B-003,25_516582,25-00000103\25-00000001.PDF

Also need C:\CAF\ removing from each line

So from this
25,516582,B-003,C:\CAF\25-00000103\25-00000001.PDF
10,516983,B-003,C:\CAF\10-00000103\10-00000003.PDF
13,516972,N-102,C:\CAF\13-00000103\13-00000004.PDF
09,516940,N-102,C:\CAF\09-00000103\09-00000005.PDF

To This
25,516582,B-003,25_516582,25-00000103\25-00000001.PDF
10,516983,B-003,10_516983,10-00000103\10-00000003.PDF
13,516972,N-102,13_516972,13-00000103\13-00000004.PDF
09,516940,N-102,09_516940,09-00000103\09-00000005.PDF

Thanks

John H