In Pega8.x there is a new feature implemented where the uploaded pdf is being shown as section.
You can check this implementation or make use of the rules used in this implementation.
In your portal Select "Documents" from the left navigation pannel and upload a pdf there. Click on Submit and you will see the pdf being shown in a section. If you will check this section is using "pxFilePreview" section which is using "pxAttachmentPreview" control to display the pdf.