To find all notes that contain a PDF file within them, use the search query:
This can be useful if you want to, for example, create a saved search of all your product manuals. Let's say you tag all your products with the tag called
Products, and that for many of them you find a digital version of their manual online (which is virtually always in PDF format) and attach it to the note. You can create a saved search consisting of the query:
Products resource:application/pdfand call it Product Manuals.
For more information about the resource filter, see the Evernote API documentation. Application/pdf is the mime type for PDFs. For a list of other mime types, see this excellent reference page.