Your problem is very genuine, and you basically want to have a scanned image turned into a pdf and then editting that. Well, its a complicated situation. And then follow the steps.1) Open scanned pdf file in classicPDF. 2) Go to edit and click 'move/resize' in image tab, and export the picture (whole document will look as picture as you have scanned document) to picture format out of the pdf file. 3) Search for OCR(optical character recognition) software and use it to read the text from your exported images. It will do so and give you result in an MS word format. Make your changes in it, and then you can convert it back to PDF. 4) However if you need to make some slight changes to the document, its easy and just open your file in classicPDF editor, click insert text and then click where you want to make changes, you will get a text box, write in it, and when you are done with editing, save it. The box will overwrite what was beneath it. There is a bit complication involved but this actually involves the conversion of image to text, which can be done through OCR only. but this will make you able to have a simple pdf. Resource link
You can find free software here — click on the image to download.