1. We are starting with 2 layers representing 2 pieces of paper. The lighter paper on top and the dark on the bottom.
2. A Grid Snap drawing guide has been created to make selecting the exact areas easier. However the Grid Snap is not required to do this.

1. Make sure the top layer is selected.
2. Select the Polygon Mask tool.
3. Draw the outline of the area that will be the corner.
4. Press the Done button.

1. The mask is created but we want to invert the mask so that the mask covers everything except the corner.

1. Select Invert Mask from the Mask menu.

1. Select the Copy Tool.
2. Draw a rectangle around the corner.

After releasing the mouse button the paper corner area will be in the clipboard.  Optionally safe it to the Clips panel if you are worried about losing it.

1. Use the Clear Layer command to clear the paper corner.
2. Notice the corner is gone but the rest of the top page was protected by the mask.

1. Select Clear Mask from the Mask menu.

There are a number of changes in this step but follow the numbers.

1. Create a new layer. This is where the folded corner will be place.
2. The top page layer is hidden so that the corner can be visually placed properly
3. The Paste Tool is selected.
4. Select the Stamp mode of the Paste tool.
5. Enter 180 for the Rotate value since you want the clipped corner rotated. Do not change the size, this should be the size captured.
6. Place the corner in the correct location by clicking and dragging.

1. The Drop Shadow filter is used.
2. Notice we show the top page layer so we can see better how the drop shadow will look.
3. Adjust the sliders to get the effect you like.
4. Nice results
5. Press the Apply button.