Here are a few links to sites that may be helpful to you.
Although a significant amount of editing and proofreading is now done using tools such as Microsoft’s track changes feature and Adobe’s commenting tool, we use traditional proofireading marks and symbols if the client prefers them.
Adobe Acrobat Reader DC software is the free global standard for reliably viewing, printing, and commenting on PDF documents. It’s the only PDF viewer that can open and interact with all types of PDF content, including forms and multimedia. Get it free here!