Like turning pages in a real book, these buttons move the reader forward and back through the PDF document. The exact order of the documents page are followed by using these buttons.
These buttons take the reader either to the first or last page of the document.
The buttons remember the order of the pages you viewed. When the reader pushes "back", the previously viewed page is shown. Assume the reader was on page 10 and jumped to page 20. When the reader pushes "back," page 10 will be shown (not page 19) because page 10 was the previously viewed page.