The built-in document edit view has the capabilities of adjusting document boundary, adjusting the brightness and contrast of the detected document, converting the document to a color/gray/black-and-white document, etc.
You can adjust document boundary by dragging the corners.
All the editing features are built into the icons. As you can see, there are icons for rotating a document. You can simply click them to rotate the document by 90 degrees clockwise or counter-clockwise.
Likewise, you can click the icons to adjust the brightness and contrast of the document or convert it to a color/gray/black-and-white document.
If you do not want to use Dynamsoft's UI, there are functions available for you to work out your own UI.