Cannot Edit PDF of Combined Files

I am working with Adobe Pro in a professional setting. I have a dozen photos that I need to send to another party that must go in PDF format.  The original image file is JPEG, so I converted all of them to PDF and combined the files so that I had one PDF with all images in it. Normally, I would be able to use the tools on the right side of the frame to apply a bates stamp to the file, but the combined file has no tools--they are all greyed out and only show up when I select "Tools," not on the right side like normal.  I am able to apply stamp to individual PDF files, but not the combined file.  This only seems to be the issue b/c these are images, not documents, b/c I've never had an issue combining multiple documents into one PDF and stamping them all at once. 

Any advice is appreciated.