Why is the capture not triggered automatically?
Lay the document on a high-contrast background withdocument and try to flatten it. Then the scan will triggered automatically in most cases.
The recognition algorithms of PaperScan are looking for edges of your document. The algorithms rely very strongly on contrast, so a white sheet of paper on a dark table is ideal. Another key factor is the quality of your original. You should be able to recognize a set of four edges where two are relatively parallel to each other. If you can`t, the algorithms have a hard time recognizing the edges.
PaperScan is optimized for iPhone 5. If you install it on an anterior model, you may have to capture scans manually and deskew the images by hand.