When you open a picture in Photoshop and edit the brightness and contrast, for example, an adjustment layer is created and added on top of the photo layer with the edit. So, if you need to copy that photo along with the brightness and contrast adjustment to paste it into another Photoshop window, you can do it quickly by merging them into one, enabling you to work with a single layer again.
How to merge layers in Photoshop
Step 1: Select layers to merge
Let’s merge the type layers in this example, as well as the gray rectangles behind the letters. These include “FOR SALE,” Rectangle 2 copy, “FIRE TV,” and Rectangle 2. So we will select these four layers to merge.
Step 2: Merge layers
To merge these layers, you can press Ctrl+E (Cmd+E for Mac) or right-click (Control+click for Mac) on the selected layers and click Merge Layers. When layers are merged, essentially they are flattened into a single layer, so you won’t be able to work individually with them. Merging layers is best when you’re already done working on those layers and still need to work with others in your file. To merge all the layers in your Photoshop document, select all the layers and right-click (Control+click for Mac) on the layers panel and select Merge Layers or, without needing to select them, use the shortcut Shift+Ctrl+E (Shift+Cmd+E for Mac). Photoshop also has the option to merge visible layers. This will combine just the layers that are visible in the moment and leave others that have the visibility off, separated. Just right-click (Control+click for Mac) on the layers panel in Photoshop and select Merge Visible.