When I get email docs, I save them all to the client's current year folder, as they come in. And if the email contains any useful info, I print the email to a PDF in the same folder.
Good naming conventions help keep this files organized (22 W2 X company, 22 1099R Z corp, etc.). You can merge them all into one PDF and rearrange the pages, or work with them as separate PDFs.
All PDF viewing software has some ability to type on the PDF. I usually put a dot with pen tool by clicking or type some text or paste in an adding machine tape, like we used to do with actual tape and actual adding machine tapes. Electronic is far superior. I also draw arrows or ovals or rectangles around important data to make it easier to see for when I'm reviewing a return.
I was always holding paper docs up in one hand to read them, now I just have them on another monitor, and zoom in as needed to read smaller text. Used to use a magnifying glass.
And if a document is searchable, I can copy/paste EINs, SSNs, or amounts from the docs into the software. I prefer to copy/paste ID#s and addresses so there aren't any typos.
And I just convert photos of docs to a PDF, after cropping, resizing and enhancing if needed. This work replaces going through paper records, removing staples, rearranging, etc. Clients who do better jobs of organizing and properly scanning their records, are rewarded with lower fees.