**Describe the bug** Flake 8 lint warning from `pdf_watermarkadder` and `video_cropper`. - `pdf_watermarkadder`: missing whitespace after ',' on line 26 of main.py. - `video_cropper`: Didn't use isinstance() for checking if an object is an instance of a class or type **To Reproduce** Steps to reproduce the behavior: 1. Create virtual environment and activate it 2. `pip install flake8` 3. Go to `pdf_watermarkadder` (or `video_cropper`) folder 4. `flake8 main.py` (if you are in `video_cropper`, `flake8 video_cropper.py`) 5. See error **Expected behavior** My pull request should pass flake8 lint check. **Screenshots** If applicable, add screenshots to help explain your problem.  **Additional context**