I am displaying all attachments in a
Visualforce Page with
renderAs="pdf". It displays the attachment if it is an image but not if it is a pdf. I am using an iframe
to show the pdf attachment but it is not working within a pdf. Is it possible?
It's not possible to render a PDF that contains another PDF inside of it. The Salesforce PDF render engine can't render a Blob image. Any images need to be standard formats such as JPG, PNG, GIF, or TIFF images. There might be a few others that are supported as well, but definitely not blobs.
An existing PDF will essentially contain a wrapper around a JPG along with additional information about how to display and print it.