Use Preview’s Instant Alpha feature to erase backgrounds in images or make certain parts transparent. Start with a base image.  In this example, I use a picture of the Minneapolis skyline and will try to remove the fog/clouds on top of the building. Open your image in Preview.

You can add your signature to PDFs using your Mac.  Sign official documents using your own hand-written signautre.  Sign business letters, tax forms, or any other document requiring your signature. I rarely have access to a fax machine and have found that most places will accept my documents when signed