1. Open the start menu and search for Control Panel

2. Select View Devices and Printers under the Hardware and Sound heading

3. Select the printer you want to add the size for and go to Print Server Properties

4. Select a form type you wont need to use (We recommend something like Japanese Postcard Rotated) and tick the Create New Form box.

5. Now rename the form and manually enter the page size you need below.
Here are a few standard page sizes for quick reference:
Paper Size | Inches | Millimetres |
A1 | 23-3/8 x 33-1/8 in | 594 x 841 mm |
A2 | 16-1/2 x 23-3/8 in | 420 x 594 mm |
A3 | 11-3/4 x 16-1/2 in | 297 x 420 mm |
A4 | 8-1/4 x 11-3/4 in | 210 x 297 mm |
You can now return to whichever app you needed to print from and will be able to find the new page size that you set listed in the Printing Preferences menu.
Thanks for reading this guide on how to add paper sizes to a PDF printer, I hope it’s of help to you.