Using Homebrew to convert TIFF to PDF
The * in convert *.jpg output.pdf expands to the list of inputs. This means the command you were actually running looked like:

convert one.jpg two.jpg three.jpg output.pdf


As you can see from this, that's not what you want, since all the images will be compiled into the output PDF. Also, as the command contains ‘jpg’, it looks for ‘jpg’ files, not ‘tiff’, so you need to change this too.

Therefore, you need to run that command for each of the inputs.

find /path/to/folder -iname "*.tiff" -exec convert {} {}.pdf \;