Check out this past thread for troubleshooting steps: Picture Container goes blank in preview mode
Also, a PDF file may not be compatible to display in preview mode, so there may be no solution. In that case you should export the PDF to a temp location and open it automatically so the user can print it out like any other PDF.
Re: "I am trying to display pdf file from server in the web container fleld."
There is a Web Viewer and a Container Field. It is possible to view images in both. Which are you referring to?