PGN-Editors

ChessX Chess Database and PGN viewer
ChessX is an open source and free chess database application.
Features
- Load and save PGN files
- Work with multiple databases simultaneously
- Browse chess games, including variations
- Enter moves, variations, comments
- Setup board, copy/paste FEN
- Search in Databases for text or positions
- Display tree of moves for the current position
- Analyze using UCI and Winboard/Xboard Chess engines
- Prepare for openings or opponents
- Training mode (next move is hidden)
- Integrated Stockfish engine
- FICS Support
Caissa's Web: PGN Editor

This is a free online pgn-editor, easy to use
Penguin Chess PGN Editor 14

You can download the Penguin Chess PGN Editor 14 for free and install it on your local computer.
Notepad++

Notepad++ is a universal, very advanced and easy-to-use text-editor, not only for pgn. I recommend this editor to create the pgn-file for upload in the CLM3.