I would look for a PDF API like I Love PDF or PDFKit and implement that but it all depeneds on ability. It might also be possible to add the images to a Google Doc and download the doc as a PDF.
That makes it a bit more complicated, The first thing to do would be to merge the items so you have one item that contains multiple binary items then maybe have a switch node that goes out to a multiple http request nodes that are configured to handle different amount of binary items.