1. Add the Content Editor Web Part to SharePoint Page. Then Add a “Content Editor Web part” to your SharePoint page. Now clicck on the “Open the Tool Pane”, click on “Source Editor” to place the HTML source.
2. Place the following piece of code in to the Source Editor:
The src goes to the location where the pdf files are stored. It can be in document library or a UNC Path.
3. Make sure pdf client is installed in the client machines .
You may find interesting to read: How to show movie files in SharePoint Pages
Attempt a question on Web Parts: Question on Web Parts