How many are you trying to combine, and are they structured data (like logs) or plain prose ? Combine text into one cell in Microsoft Excel
This directs the contents of all text files into a single merged.txt file.
Use the TEXTJOIN or CONCAT functions to merge strings from different cells.
If the text files contain data like columns or lists, you can combine them in or Google Sheets :
Example: =TEXTJOIN(" ", TRUE, A1, B1) will combine cells A1 and B1 with a space between them.