Hi, Ich'har.
Thanks for sharing your problem. As you see, there are many free conversion tools online. But I don't suggest you to use them to do with your conversion work. Because I always believe that the free tools online do not have so many professional functions as the paid ones. And it is said that some of them might contain some virus. Check some free trials of the paid professional conversion tools to convert pdf to image using C#.NET first before you make your final decision if possible. I also suggest you choose one whose way of processing is simple and fast. It can save a lot of time for you. Remember to do your conversion work according to its tutorial page about Pdf conversion. I hope you success. Good luck.
Best regards,
Lee