PDF export from Pages document
Unfortunately Apple's PDF export doesn't create the standard PDF Table of Contents, you'll need to use other software to add one to your existing PDF.

There are a variety of options at a variety of prices:

OpenOffice Writer: A hassle, but it's the only free option I've seen. You'd export your Pages file as Word or rtf and then open it in OpenOffice Writer and then export to PDF; it will generate a PDF table of contents as part of the export.

PDF Outliner: Just $4.99 in the Mac App Store, it's probably the best combination of cheap and easy. It's specifically designed to add a PDF Table of Contents to your document.

PDFpenPro: At $99.95 it's not cheap but it does pretty much everything the full version of Adobe Acrobat does and is much, much cheaper.

Acrobat X Standard: The real thing from Adobe for "just" $449.95. If you only need to do this now and you'll be done creating PDF Tables of Contents within 30 days you can download the free trial. After 30 days, though, you're out of luck.