If I’m not mistaken this is not possible. On the desktop version of Scrivener you can highlight text in a PDF and normal text documents, but on the iOS version you can only do it in text documents.
I don’t know how difficult this is, considering that a lot of pdf-apps have highlighting features, but it would be cool if we could highlight in PDF’s on the iOS version as well.
Most of my research-reading happens on the iPad, on the iOS version, and having the ability do to it on that device, would be great.
It’s not trivial for a program that isn’t a PDF reader. If the OS didn’t have a viewer, Scrivener wouldn’t be able to display PDFs, lets just put it that way.
If Apple adds highlighting to their PDF viewer (which actually technically isn’t even that, it’s a Web viewer within which they have encapsulated a PDF displayer, so don’t cross your fingers) in such a way that third-party tools like ours can tap into it (like on the Mac), I am sure we’ll make it possible to do so in Scrivener.