Hi Bill,
To be able to parse images to retrieve scanned text, you must first parse the image or the PDFs using an OCR (Optical Character Recognition) engine.
ServiceNow doesn't include an OCR engine.
Some softwares, like Adobe Acrobat Pro DC, include one. Some scanner drivers now automatically do OCR you the scanned document. Usually, OCR software requires the image resolution to be at last 300 dpi, so you may have to check the resolution of the image included in your PDF.
If your images are 300dpi or more, my recommendation is to put all your old PDFs thru Acrobat Pro or another OCR software. (Procedure here: Batch OCR multiple PDFs in Acrobat DC )
Once your PDFs are updated, they will be searchable and indexable. (The text is added as an invisible layer on top of each image).
The good news is that PDF attachments are searchable and ServiceNow will recognize and index your updated PDFs. Any OCR'ed PDF attached to a KB will be included in the search result. (Source: Feature to Import a PDF Document? )
The bad news is that you have about 4000 documents to process thru OCR and re-attach to your KB 😕
