@echo off

:: Var
  set last=0
  set line=0
  set dest="%~n1 + %~n2.txt"


setlocal
:nextline
  call :writeline %1
  call :writeline %2
  set /A line+=1
  if %last%==0 goto nextline
endlocal
goto :EOF


:writeline
  if %line%==0 (set "skip=") else (set "skip=skip=%line% ")
  for /f "%skip%tokens=*" %%a in ('type %1') do (
    echo %%a >> %dest%
    exit /b
  )
  set last=1
  exit /b