Adding a custom cover/back page
Open the storyboard that you'd like to export. Click Download above your storyboard and select PDF from the dropdown menu to access the PDF exporter.
Select the Front cover tab on the left-hand side.
Select the Use custom front cover option.
Select Upload new PDF and search for your cover page.
To upload a back page, click the Back cover tab on the left-hand side.
Both front covers and end pages are specific to each storyboard, so changing them for one storyboard won't change the covers for any of your other storyboards.
To learn how to change the display of cover & end pages, take a look at this article.
Supported formats
Cover and back pages can be multiple page PDF documents if you wish, but they should be:
A4 in format (other sizes will be stretched to fit)
Basic PDF documents (optional content or interactive PDFs are not supported)
No more than 10MB in size
Repairing malformed PDFs
If you see an error after generating a PDF indicating that you have a malformed PDF cover or back page, a possible solution is to re-export the cover/back page, then upload it again.
On Mac, you can do this with Preview by going to File > Export as PDF... in the menu.
On Windows, you will need a PDF reader (such as the free Adobe Acrobat). Once you've downloaded that, just save out a new copy of your cover/end page and replace the existing file.