If you have a PDF document on the web and you want to draw the attention of your friend to a particular page in the document, you can send him a link to the page and also tell him the page number to look at.

But there is a more convenient alternative. You can actually add a reference to the page when you send the link which will open the particular page instead of the first page. You can do this by adding the parameter page=<pagenum> at the end of the link.

Here is a live example.

http://www.verypdf.com/pdf2htm/example/sample2.pdf#page=4

Clicking on the above link will open up the fourth page automatically. There are more such parameters that you can use. For instance, you could add the parameter zoom=<zoomvalue> to open the pdf at a particular zoom level.

http://www.verypdf.com/pdf2htm/example/sample2.pdf#zoom=50

For more parameters, check out Parameters for Opening PDF Files (PDF) in the Acrobat SDK documentation set.