You can simply remove the background of your signature via Microsoft Word.
- Make sure you’re in the Picture Format section of the top bar
- Click “Crop”, in the “Picture” tab, to remove any unwanted edges.
- Click “Corrections” → Click “Picture Corrections Options” → Set sharpness to 100% and Brightness to 60-90%.
- Click “Colour” → Select this colour filter to make it full black (or another colour filter for other colours!