words – Replace new lines with a comma delimiter with Notepad++? – Stack Overflow

Open the find and replace dialog (press CTRL+H).

Then select Regular expression in the ‘Search Mode’ section at the bottom.

In the Find what field enter this: [\r\n]+

In the Replace with: ,

There is a space after the comma.

Source: words – Replace new lines with a comma delimiter with Notepad++? – Stack Overflow