Getting Started
Open the Custom Page Sizer by going to:
Extensions → Page Sizer by Adam Natad → Start
Export or Download Note
NOTE: Do not export or download directly to PDF from Google Docs as this may cause incorrect page dimensions. Instead, export your document as a .docx file by selecting File → Download → Microsoft Word (.docx). Open the file in MS Word, verify the page size via Layout → Size → More Paper Sizes…, and then convert it to PDF.
Google Default Page Setup
WARNING: Setting a custom page size that is not officially supported by Google Docs may cause the default File → Page Setup option to become unusable. To restore access, use this add-on to switch back to a Google-supported paper size.