Drag layers between tab-docked documents in Photoshop
Using Photoshop CC (on Windows), I sometimes need to drag layers from one document to another. When the documents are tab-docked, I expected to be able to drag the layer over the tab and have have it "spring" open (as with folders on OS X). This does not work for me, however, and I instead have to undock one of the documents involved so that I can drag the layer onto the content of the document I want.
dragging layer over tab and holding does not bring tab to front
There's a slight trick to it.
You can't drag from the layers panel to a tab.
Highlight the layers you wish to move in the Layers Panel then click drag from the document window to a hidden tab. The tab should then spring forward and allow you to "drop" the layers.
Basically the drag has to be initiated from within the active tab in order to get the hidden tabs to pop forward.
Also you can right click on selected layer(-s) and use Duplicate layer option