The saved documents will be based on Adobe's Open Specification and can be read using any tool that can view PDFs.
The PDF support will be built into Word, Excel, PowerPoint, Access, Publisher, OneNote, Visio, and InfoPath! I love how well this new functionality will work in combination with the new Open XML formats in Word, Excel, and PowerPoint. We've really heard the feedback that sharing documents across multiple platforms and long term archiving are really important. People now have a couple options here, with the existing support for HTML and RTF, and now the new support for Open XML formats and PDF!
This really all comes down to the basic theme of content sharing. We realize that this is a really important scenario, and that's why we're making the move to default XML formats that are fully documented. Now we've moved to the files being in open, redistributable, and archivable formats; and we can focus more of our innovations around ways to act on those formats. This is true on the client and the server.
Read More about Pdf support on Office12 here
Also Microsoft’s Steven Sinofsky Discusses Support for the PDF Format in Office “12” on Microsoft PressPass
Update on Oct 4: Nice article posted on PCWorld "Office Improves PDF Support"