If you want to make one pdf-file that exist of multiple A4 pages with one each page a jpg-image.

Create a directory and drop all jpg images in that directory.
Launch this command in that directory

convert *.jpg -resize 575x823^> -bordercolor '#ddd' -border 5x5 -page A4 -background white -extent 595x842 "FILE NAME.pdf"

Running out off disk space on you mobile device like Tabled, Phone of laptop and because of the big file size of your photo files? But you do not want to delete your photos? Resize them to small files.