images in pdf - colorspace=?
If an image is copied from Acrobat Reader DC and pastes as RGB, is it possible to get the original color space?
Well firstly you shouldn't copy and paste it, but extract using xpdf or simply open it with Photoshop directly.

But yes, you can assign a color profile in Photoshop (assuming the original is some kind of RGB, not CMYK. Otherwise it would be no way to 100% recover the original color. Approximation is possible though.) or similar software.

Please show an example if you have further questions.
Oops, forgot Photoshop could do that. Thanks.