I wonder if you want something that isn’t available in Linux. Years ago I had a Hewlett Packard program in Windows that created text PDFs. However, I don’t know of a Linux program that does this. Instead, you have to use an OCR like cuneiform or tesseract to extract the text and then put that text in a PDF. I usually do that by coping the text directly from tesseract into LyX and then creating the PDF. Of course, you lose the formating in the original document.
As jonte1 says, I think you need to explain exactly what you want.