If your files are in the correct order, in Windows you can combine all the txt files with a simple "copy *.txt All_files.txt" If they aren't in the correct order, you could use a for "FOR /L" loop.
FOR /L %%parameter IN (start,step,end) DO command
or a simpler:
copy file1+file2+file3 All_files.txt
and keep appending the files to the end.