We want to start with a background image or color in the background layer, and then add a new layer, create a selection for the paper and fill it with white. We should have something like this:
Now we can deselect (Ctrl+D) and then goto Edit > Transform > Warp. We want to make it look like this:
Next, we want to make a selection like this:
Now make another new layer and fill this selection in any color. Now Ctrl-click the layer we just created to make a selection of the square, then hold Ctrl+Alt and click the sheet layer. We should get the following:
Make sure we're on the new square layer and hit Delete. Now Ctrl-click the square layer to get this selection:
Goto the sheet layer and hit delete. We should now have something that looks no different, but the top right of the sheet should be deleted underneath the corner layer. Now hide the corner layer and clean up the corner of the sheet:
Now we want to make a new selection to delete part of the corner layer. Make a selection like this:
Then show the corner layer, select it and delete the selection:
Next, goto the layer styles of the corner layer and choose Gradient Overlay. We will use a gradient like this:
You might also want to alter the scale and position of the gradient (change the position by dragging it around on the canvas while in the gradient overlay settings). Also, change the angle of the gradient to somewhere around 50. We should also add a Drop Shadow, 50% opacity, distance 0 or 1px, size 5-10px.
We can also add a drop shadow to the sheet too:
Another option is to make a selction like so:
And delete it from the corner layer:
More Tutorials: 
