If you want to extract highlighted text from PDF file as a plain text file, then this post covers some good free PDF Highlight Extractor software to do that.

If you want to extract Tables from PDFs, then there are some free PDF table extractor tools that can help you do it easily. Take a look!

If you're wanting to convert an image into text, Google Docs has a powerful Optical Character Recognition feature built right in. Here's how to make it work.