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.