Merge two documents

What operating system?
It should work:
C:\>copy File1.txt+File2.txt FileNew.txt

See Windows copy command help below:

Microsoft Windows 2000 [Version 5.00.2195]
(C) Copyright 1985-1999 Microsoft Corp.

C:\>copy /?
Copies one or more filesto another location.

COPY [/V] [/N] [/Y | /-Y] [/Z] [/A | /B ] source [/A | /B]
[+ source [/A | /B] [+ ...]] [destination [/A | /B]]

source Specifies the file or files to be copied.
/A Indicates an ASCII text file. /B Indicates a binary file.
destination Specifies the directory and/or filename for the new file(s).
/V Verifies that new files are written correctly.
/N Uses short filename, if available, when copying a filewith a
non-8dot3 name.
/Y Suppresses prompting to confirm you want to overwrite an
existing destination file.
/-Y Causes prompting to confirm you want to overwrite an
existing destination file.
/Z Copies networked files in restartable mode.

The switch /Y may be preset in the COPYCMD environment variable.
This may be overridden with /-Y on the command line. Default is
to prompt on overwrites unless COPY command is being executed from
within a batch script.

To append files, specify a single file for destination, but multiple files
for source (using wildcards or file1+file2+file3 format).

just take out the spaces between the multiple source files...
example:
copy file1+file2 filenew