- Open a CLI terminal on the folder with all the file you want to merge.
- Copy and paste the following command:
$ copy *.html output.html
This command will select all the text (.txt) files in the directory and output them all merged together into the new text file called output.txt which you can rename to whatever you like. Echo each new line after reading each file, as every new file written to the merged file will start at the end of the last current line.
Via: http://www.wikihow.com/Merge-Text-(.Txt)-Files-in-Command-Prompt