If your file is that big then you are, as Wayrad suggests, making a PDF file of images. You will need some OCR software to convert the PDF to searchable text. Then you will need to edit all the OCR errors that will creep in.
Check the software that came with your scanner. There may be a copy of ABBYY Sprint, or an early version of ABBYY Fineware, or maybe Omnipage.
(I invested in ABBYY Fineware 10, which does a good job but is quite expensive.)
Here's an old thread that may just help:
https://www.mobileread.com/forums/showthread.php?t=9780
You may want to re-post your question in the Workshop forum, where you will get more up-to-date advice on scanning and OCR issues.