Also kindly explain how the following methods affect the annotations created.
Pause and resume relate to the background rendering threads. The idea here, is that if you want to have multiple tabs for viewing different docs, but only one document is actually viewable at a time, then you could stop the other tabs from taking up processor time.
As for update, that is used to force PDFViewCtrl to re-render tiles. However, this version of Update redraws everything. There are other overloads for Update that accept page numbers and rectangles, so that only specific regions are re-drawn. You can check out the Tools source code for example usages of update.
For example, if you added, or removed, an annotation, you would call mPdfViewCtrl.update(new_annot, page_num).
If you look at the Tools project you can see examples of usage.