First when opening multiple PDF documents in one window open Preview, Preferences, General and change the Open Groups of files in the same window default to Open all files in one window. Select a group of files, right click and choose open. All PDF’s in the selection will open in a single window.
Simply print to PDF all the documents in the single open Window
How to Sign a Document?
Click the plus button to add a new signature. Your web cam will tun on a display a video with a line. Write your signature on a piece of blank white paper and hold it up to the camera with your signature on the blue line. Once the computer captures your signature it will be displayed in the preview area. Click on to create your signature.