Well, if there is a function to somehow get that PDF url based on the custom field, then it should be possible via a custom code. This tutorial can help you to get started with.
Check this documentation to see how to enabled PDF content search and index, it will help. The PDF files need to be in the media library in order for this to work.
I tried to log-in to check the configuration, but the credentials does not work. Are the files in the media library? Is the attachment search enabled (General Options -> Attachments)?
Oh, I understand now, that is not possible – the plugin can search the attachments individually, and display them. It cannot search for parent posts based on the attachment contents, at least not yet. It is a planned feature, should be implemented later this year.