iAnnotate features two options for adjusting how your documents move on the page. These options are Scroll Lock and Elastic Scroll Lock.
To enable scroll lock, simply tap the Toggle Scroll Lock tool icon in the toolbar. It is preinstalled on the default toolbar and can also be found under the View and Utility tabs in your Toolbox. The padlock icon will appear closed when the tool is in use.
Scroll Lock simply locks the page's horizontal orientation, preventing the pages from moving side-to-side. This option is ideal if you want to maintain a consistent viewing range on each page.
Elastic Scroll Lock
The Elastic Scroll Lock option can be found under App Settings > Reading. You must have normal Scroll Lock enabled in order to use this feature.
Elastic Scroll Lock lets you scroll over the edges of pages to a certain point. At that point, the document "bounces back" to its scroll-locked position. This option may be useful if you have a widely-formatted page on which you need to view additional content or markups at the edges.