Transparency

There is not anything special about pasting with transparency. If the copied image has transparency, it will be pasted with transparency.

But I copied the image with transparency and it pasted without transparency!
Any solution?

If you show us the image you copied maybe we can help. Just upload it to imgur or equivalent.

What app are you pasting it from? If it's not RW-Designer, it may not work.

I was learning to use Photoshop for a class, and I found that the same thing happens trying to copy and paste images from Photoshop into RW-Paint. If the Photoshop image had empty space, copying to Paint will result in a black background, and vice versa. (Maybe incompatible transparency format?)

Yes, Photoshop uses its own custom (and nowhere documented) way of copying transparency. It is understandable, as in earlier Windows, there was no standard way to do it. Now there is and RWP is using it. You can for example copy image with transparency from Firefox and paste in into RWPaint.