In my email program, I open the newsletter, then use File Menu --> Export as pdf. It's Apple Mail on a Mac. Or I just tell it to print, then in the bottom left corner, scroll to Save as PDF. On Google gmail, I open the newsletter, then File --> Print, and in the print dialog box, I click on CHANGE for the printer destination, and select Save as PDF. Those are the only email programs I use, but I'm sure all of them have a Save as PDF capability these days.
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