You can copy all of an image's layers into another open image by dragging the image thumbnail from the Browser onto the open image.
To use the Browser to copy one image into another:
Open the image into which you want to copy the layers. This target image must be a 16 million color or greyscale image.
On the Layer palette, click the layer which you want to place the new image above.
Open the Browser (choose File > Browse or press Ctrl + B).
Navigate to the folder containing the source image (the image you want to copy.)
Click the source image's browser thumbnail and drag it into the target image. When you release the mouse button, the layers are added to the image. They are linked automatically.
Note: If a new layer duplicates the name of a layer in the target image, a number is appended to the name.
Pasting a Cut or Copied Selection as a New Image
Pasting a Cut or Copied Selection as a New Layer
Pasting a Cut or Copied Selection into a Layer