this report has been filed here:

https://bugs.launchpad.net/ubuntu/+source/evince/+bug/796188

"I'm curious whether it's possible to add a feature to evince which allows the user the following:

1. select the screenshot tool
2. select a specific area of the document with your mouse (a rectangle: press to start selection and release mouse button when finished)
3. the selected area will be saved to the clipboard as an image which can be pasted e.g. in Openoffice.org Writer or comparable office software

I'm inquiring about this feature because I know it from Acrobat Reader and it's the last feature that's keeping me from uninstalling Acrobat. I know a lot of people at university who use this tool on a regular basis when creating summaries of lectures. It's a very pleasant way to copy & paste important parts of PDF documents, mainly diagrams and illustrations and imo this won't be too much of a hassle to implement.

I attached a screenshot of the desired functionality as observed while using Acrobat Reader. I hope this clears it up a bit.
"

Acroread:

https://bugs.launchpad.net/ubuntu/+source/evince/+bug/796188/+attachment/2166315/+files/evince%20feature%20request.png