Is there any way to limit customers canto only upload single page pdf's?

No, it is not possible to limit the users from uploading a file that has multiple pages through File upload (Product Upload and forms) or FTP file upload. As an alternative, you can use an option of e-Doc Builder Product, if you want to limit the user from uploading a file of specific number of Pages. In order to do that you can

 

Because the Master PDF has limited number of pages, if the user uploads a file that has more pages then the template has, e-Doc Builder will ignore other pages. For Ex, if you have uploaded a single page Master PDF and created the template and if the user uploads a file that has two page, the 2^nd page will be ignored.

 

The user will be able to see the Preview as well and can determine if the user would like to go ahead or would like to change the file to have appropriate number of pages.

 

Please Note: This alternative will not limit the user from uploading a file that has more or less number of pages, however, it will only show specific number of pages once the file is uploaded on Template