I wanted to save a free comic I found online but there was no pdf available only a zip file of pictures, so I downloaded and extracted the pictures then viewed them in Gallery at the same time in split screen I had the Samsung Notes app open on a new note. Viewing one picture at a time I just pressed on the one I wanted and when I got what looked like a small copy I dragged it across to the note were it was pasted. This worked fine and I was then able to save the note as a pdf.
This might help you with your problem.
