I found a very useful program for creating PDF files from scanned documents

Linux tip: I found a very useful Linux program for creating PDF files from scanned documents. It's most useful feature is that it uses OCR software to create text from the images and adds it to the PDF file.

You will have to install the following

gscan2pdf
ocropus (OCR software this one overlays the text on the image, tesseract doesn't do this)

It can also help you crop pages, improve the scanned image (for example if it's from a book) etc..

You can import PDF files and apply any of it's features. In the attached photo I imported an old book that was scanned but didn't have text embedded in it.