If you give a link to the PDF on the web page, any browser will be able to download the file and then the user can open it in a PDF viewer of his choice.
If you want to embed the PDF document in a web page, then the browser needs to have a PDF plugin installed. This may not be the case with all browsers. The PDF will be displayed only if the PDF viewer application's plugin is registered with the browser.
The other way of embedding the PDF document is to use a server-side component that renders the PDF as ordinary HTML web page elements. Google has an embeddable PDF viewer.
Google Docs offers an
undocumented feature that lets you
embed PDF files and PowerPoint
presentations in a web page. The files
don't have to be uploaded to Google
Docs, but they need to be available
online.