Hello,
I gather you have printed the PDF to a desktop printer. Acrobat has simply shrunk the PDF to fit the printer default setting
Go File - Print, and you should see the print dialogue window. The first line of this box should say "Printer". The second line should say "Presets".To the right of the "Printer" name are up-down arrows, and to the right of that is a larger down arrow.
Click on that and the window opens up, and one of the options is "Page Scaling", and that may say "Shrink to Printable Area" as a default setting.
As an example, my desktop printer is A4 and an A4 document will print out at 93% by using this default setting.
Simply click on "Page Scaling" and select "None" to get full size.
If your newsletter is going to be sent to a printing company at the end of the week, then you have nothing to worry about.
Hope that helps.
Phil