Merging files (.txt) or files that we usually open with the Notepad application can be done with CMD (Command Prompt).
If you need to manage a lot of data in a very large number of rows (more than one million rows), you can use notepad.
Because Mircosoft Excel, as we know cm up to 1 million rows.
Exactly I kind of forgot hehe.

Here’s how to merge Notepad (.txt) files that I found on Yonathan Gunawan’s blog.

Combining a group of TXT files to become just one TXT file can be done by using the copy command via Command Prompt (CMD).
The method is as follows:

1. Open Command Prompt.
   Click the Windows Start button, click Run, then type cmd and press Enter.
2. Enter the folder containing the set of TXT files you want to merge.
   Use theCD (Change Directory) command to change the path in the Command Prompt.
   CD C:\Data folder that you want to merge data\
3. Type copy *.txt data.txt and press Enter.

The above command will generate a data.txt file which is a combination of all TXT files.

Ref: yonathangunawan.wordpress.com