How can I convert a PDF file into a text file without using any library (like GNUpdf etc.) in C?
Look into how pdf’s store data inside them. Googling for 3 hours will get you exactly what you need.
Also, pdf’s store more than just text, so you’re gonna have to discard a lot of information. And the text isn’t stored in plaintext, so you’re gonna have to figure out a way to decode all the information in it. After spending days, you’ll realize what a huge waste of time this is, so you’re gonna end up using the library itself.
Don’t bother reinventing the wheel on this one. If you want to do something that involves converting a PDF into a text file, just use the library, It’d be a huge waste of time making your own library.