If you have all of your content on one page, but you want to print on multiple pages, make sure that your Page Setup under the file menu has the page size that you’d like to use and the orientation, along with the scale percentage to define how large each page is. Then from the Print dialog there is a Save as PDF drop down. That should show you the number of pages expected in the preview of the print dialog. If the number of pages is incorrect, change the page setup options until you have the size you want in the print dialog.
If you want each canvas to be a seperate page, choose File>Export, then on the PDF tab choose “Entire Document”. If you are using OmniGraffle 7.5, you will see a preview on the right of your export panel which has arrows. You can arrow through the pages to see how they will export.
OmniGraffle Pro Only: If your content is all on one canvas, you can create artboards. If you are new to artboards, there is a video at https://www.omnigroup.com/video/set/omnigraffle-7-for-mac/live-session-artboards-in-omnigraffle-7/ and a manual page at https://support.omnigroup.com/documentation/omnigraffle/mac/7.3/en/using-artboards/ which may help. The simplest way to add artboards, in my opinion, is to select the graphics you want to export together, then choose “New Artboard Under Selection” from the context menu with control + click. Once you create artboards, you can check the “Export from artboards only” checkbox when you export to PDF in OmniGraffle Pro. Under Paging, choose Multi-Page. This will give you the most precise control of which areas export, regardless of your canvas size, because you can specify the artboard geometry and edit it using the Geometry Inspector.
If I’ve missed anything, or that doesn’t get you the correct PDF export you were hoping for, please contact us by email at firstname.lastname@example.org, or if you prefer to include your document, by choosing Contact Omni from your Help menu. We are happy to help out!