You can actually copy all files to one without moving to a new location. You can choose to copy and concatenate all files by removin echo before desired command. I set to copy all files to new directory "AllFilesFolder". Please place the script in the base dir. Also - to avoid name colision (file with same name copied to AllFilesFolder), an id is added to filenames whe copiing. id is incremented for each file.
@echo off
setlocal enabledelayedexpansion
set id=0
if not exist AllFilesFolder mkdir AllFilesFolder
for /f %%a in ('dir /B /S /A-D *.txt') do (
echo copy "%%a" "AllFilesFolder\%%~dpna_!id!%%~xa"
echo type "%%a" >> allFiles.txt
set /a id+=1
)