1All hyperref/pdfLaTeX can do is insert a link of a certain form. It's up to the PDF
2viewer what to do with that link, and I don’t think there’s a standard link format
3for pages of external PDF files. Even if some viewers have implemented something for
4this, it wouldn’t be a robust solution.
5
6My suggestion would be to actually include the linked-to PDF in the PDF you’re
7creating, and then you can use features of the pdfpages package to insert hyperlink
8targets for the included pages, and then you can use internal links. A quick example:
9
10\documentclass{article}
11\usepackage{pdfpages}
12\usepackage{hyperref}
13\begin{document}
14Here's a \hyperlink{included.pdf.2}{link to to page 2 of the included pdf}.
15\includepdf[pages=1-5,link=true]{included.pdf}
16\end{document}