For example, I keep 7 years of Turbo Tax returns in a physical file. I use the online version of Turbo Tax. If I upload my paperwork to "my documents" in Turbo tax with my return, can I then throw out the original papers?
Opinion:
NO...Keep the papers.
You have no idea how many people lose access to their Online account...for one of many reason's.
They forget their passwords or their UserID...their email changed, and they can no longer get a confirmation code (when required) .... An "ex" hacked their account and changed their Password...they skipped a year?? (not sure what happens then)...and you do have to use a version with a $$$Fee every year to maintain those files..you cannot use the "Free" version. .....and, who knows if/when TTX decides to abandon those storage files.
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The original PDFs that you might have been sent to you, or you downloaded to a separate PDF file from your financial accounts...those you should keep in their PDF electronic form on your own computer BUT, you'd better back them up off computer. Once your computer crashes/dies, those files are gone.
(After tax season every year, I copy all my tax files & documents to a USB Flash drive and exchange it for one in my Bank Safe Deposit box from last year)