Preview in wrong size

@DartsNurse I just had this same issue with my sister-in-law computer. The problem often stems from a conflict between the printer driver's default settings and Acrobat's own internal settings. Even if your printer is set to A4 in your computer's general settings and you select A4 in the print dialog, Acrobat might still be pulling an incorrect default from its own configuration. To resolve this, you need to go into the specific Print Properties for the "Adobe PDF" printer itself. Access your list of printers, right-click on the Adobe PDF printer, select "Printing Preferences," and then navigate to the "Adobe PDF Page Size" or a similar setting. Here, you should be able to explicitly change the default size from Letter to A4, which should then correct the print preview and ensure your documents print with the correct dimensions. 

Also, double-check the printer's interface that the copy, print and scan is set to letter size as well!