Get ready to gat extra knowledge by this example, it will teach you how to turn a corner of the paper.
Open Image: First we have to open an image of the paper, as I have capture this image.
Selection: Choose Polygonal Lasso Tool (L key) and make selection corner of the paper, as I have done here.
Delete Selection: Now delete the selection which has been selected upper step (press DEL key).
Corner Shape: Choose Pen Tool (P key) and point three place as a corner with selected white color.
Turn Corner: Choose Pen Tool (P key) and click in between two points then try to turn something left direction to right with Direct Selection Tool (A key) as I have done here.
Inner Shadow: Go to Layer Menu > Layer Style > Inner Shadow and make setting as given below.
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