Links to PDF's can be made to target specific places in the document by appending a number sign to the end of the URL, followed by one of these:

Target a page:

page=10

So this would look like

http://server.com/title.pdf#page=10

Target a named destination:

destination_name

So this would look like:

http://server.com/title.pdf#destination_name

Thanks to the PowerPoint FAQ for this tip.
It is also possible to control what happens when the document opens - which view, what zoom, etc. See Link to PDFs from HTML -- The PowerPoint FAQ for more details.