I have several documents scanned from microfilm into PDFs. They are just text but the original pages were thin and the print on the back shows through as light gray. I can readily get rid of the gray by using a color replacer in a graphics program (I use IrfanView). This makes the page far easier to read. But IrfanView cannot open a PDF and Adobe Reader does not offer any options to save the PDF as anything else. Is there a conversion program that works well for this purpose? Older computer running Win XP.