How to display with "\pdfjs\web\viewer.html" the PDF returned into a <iframe>.

[PRA1292]

Hello,
On client side, I have a web form (with target = an <iframe>) that list a set of PDF documents. The user can then select a subset of those documents and then click on a button to launch the aggregation of the selected documents that will be displayed in an <iframe> on the same page.
On server side, when the servlet received the submitted list of documents, it concatenates them into a single PDF and add a watermark on it before returning the PDF file.
My question is the following: How should I use/configure the "\pdfjs\web\viewer.html" to display the PDF document that has been returned to the <iframe>?
Thank in advance for your help.
Best regards,