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Well, I don't have loads of experience with PDFs, but wouldn't it be the same process as taking an image from a webpage? IE - right click, Save picture as? I don't have a PDF handy to experiment with, but the PDF context menu (right-click) might have different options that the same from a web browser, I'm guessing.
Here, give me a moment to track down a PDF to experiment with, and I'll have more info to share....
Ok, I've found 2 PDFs in my files (new computer, otherwise I'd have many more). In both cases, I selected an image, right-click, the only option available is "Copy image".
So I would say, just give it a try. BUT please be sure that there is not a copyright!
Regarding resolution, it's just going to depend on the image. If the image is a low resolution, I don't think there's any way to give it more resolution. Although I certainly could be wrong about that. I could be wrong about this too, but I think zooming would decrease the resolution, not increase it???