For easy printing at reduced scales, may I suggest Foxit Reader, a free PDF file viewer. Foxit Reader is well-known in the online paper modeling community. Besides being a great PDF viewer, it has a very easy-to-use print scaling option.
To print at a reduced scale, choose “File” > “Print”. In the “Print” window, click on the “Scale” button, then on “Custom Scale”, and enter the desired value in the % box . There is a preview window right there to show how it will look.
You can choose to print the reduced page in the center of the paper, or along the top. If you are printing at half size or smaller, you can easily print another page on the same sheet by printing along the top, then rotating and re-inserting the paper to print the second page. To print an O scale page at HO scale means printing at 55%, you might be able to fit two pages on one sheet, depending on the page margins.
If the PDF file contains multiple pages, Foxit Reader can automatically print multiple pages per sheet, although you will have to adjust the “Pages per Sheet” and “Margins” settings to get the exact scale you want (the resulting scale appears at the top of the “Preview” window).
You can get the free download here:
Disclaimer: I have no affiliation with Foxit, I’m just a paper modeler hoping to pass along some useful advice.
Thank you Paper modeling guy TM