This is remarkably easy! Create an with = hidden class and the source being your other page.

Then, create an tag with an onclick event listener:

<a class="btn" onclick="frames['frame'].print()">Print</a>

That’s it!

NB. WordPress doesn’t seem to allow iframe code at all! So without the < or > tags, It’s iframe src=”/your/url/to/print” name=”frame” class=”hide”