Dealing with Fixed Length formats both at sender and receiver side

Hi all,

I have file -- File with fixed lenght formats.

Source system will generate a text file with fixed lenght and target also needs the same file with same format.

Then we have an idea to implement the interface with out IR Development .this is fine upto now.

But now the problem is we are receiving more fields from source than we require for target process. we are not using at receiver side.

So receiving system needs only few required fields from the source file.

From soucre

Ex: Source.... DocNum Invoice No Bill date Bill amount vendor code

We require at target

Ex: Target..... DocNum Bill Date Vendor code

Please suggest me

Regards