I'll try to explain what I need because my english is terrible

I have an ASPX page where I show a PDF file (showed as full page)
When in the aspx page I raise an event, then I should change the zoom page (about 150%) and centering the showed part of my page around an object (always a textbox, but never with the same name).
I would like to know if exists a method to show only a small part of my page, defined with coordinates...
Thanks a lot!
Ale