DogEars is an Adobe Acrobat plug-in that allows you to:
Marking a pdf file with dog-ears can be compared to folding pages down in a physical book to mark your place. Once you mark a page with a dog-ear a symbol representing a turned-down page is placed on the top-right of that page, as illustrated below:
As well as using Dogears to help you locate specific pages within a document quickly and easily, you can also extract all the pages on which dog-ears have been set into a new PDF document. If you choose to do this then all the pages within a document that have been marked with a dogear will automatically be pulled into the new file: all pages that have not been marked with a dogear will not be pulled into the new file.
A tryout version of the product is available.