If you want to combine several PDF files into a single proof, you can create a single PDF file first using a free service called SmallPDF, then use that file to create a proof.
To merge multiple PDFs into a single PDF
Drag and drop the PDF files on to the drop area. Then click merge PDF.
Don’t forget to save and download your PDF file. In PageProof, drag and drop the combined file onto the file dropper on the dashboard to create a proof.