A scanned page is a picture of the page. It is not a text file. The only way to edit the picture is to cut parts out or write over it. Microsoft Paint allows you to do this. The only problem is that the text you put in often does not match the text that is there.
The other alternative is to turn the whole page into a text file. To do this software has to try and read what is in the picture of the page and convert it into a text file. The type of software that does this is called OCR software. OCR software is not always accurate and so it often misreads what is there. It is sometimes easier just to type the whole page in than to correct the mistakes of OCR software.
The best way to go is to try and find the book in text format. If it is an older book (over 50 years old), Project Gutenberg (http://www.gutenberg.org
) may have it for free.