You may have noticed that when you scan a document, it generally created a PDF but you can not copy text from that PDF. Converting that scanned PDF document into editable text can be useful for many reasons. To do that you have to buy commercial product. But now, you can convert the scanned document into editable text format without paying anything.. completely free.
Free-OCR.com is a free online OCR (Optical Character Recognition) tool. You can use this to perform OCR on any image you supply. Free-OCR takes either PDF, JPG, GIF, TIFF or BMP format. The only restriction is that the images must not be larger than 2MB, no wider or higher than 5000 pixels and there is a limit of 10 image uploads per hour.
Free-OCR.com might not be the perfect solution and can not be 100% accurate but it does the basic job.
Alternate Solution
If you own a website, you can put all of your scanned documents into a folder somewhere on your domain like "www.yourdomain.com/scanned". Google will crawl your site and once it sees the PDFs, it will give you an option to view that in HTML. Refer to Amit's article for more information.