Why not just check headers, remove header from 2nd file and append the rest to the first file?
If you don't want to use code stages that would be like:
1) Load as text files in file1, file2 data items
2) Get header from file1 (up to first newline)
3) Check that it exists in file2
4) Replace header+newline with empty string "" in file2
5) append file2 to file1
6) write result
If files are huge, you can do it with code stage without loading everything in memory.
Also in nix I'd just use tail -n +2 file2.dat >> file1.dat, there should be similar way to do it in powershell too.
------------------------------
Andrey Kudinov
Project Manager
MobileTelesystems PJSC
Europe/Moscow
------------------------------