I am not sure about PDF file but i'm sure there must be a way to do it.
What VB are writing this spftware in?
In VB6, after opening the project, press "CTRL + T" and you will be brought to the Component Dialog. From there select "Microsoft Internet Controls".
In VB.Net, there is also a "WebBrowser" control but i have never used it so you'll have to figure it out. (Should be similar to VB6)Me.WebBroweser.Navigate "C:\about.html"