Despite trying all the fixes on this board and elsewhere, I STILL get the same break running
$ /usr/bin/convert D1.JPG P1.pdf
namely:
unable to open image `P1.pdf': No such file or directory @ error/blob.c/OpenBlob/2701.
convert-im6.q16: missing an image filename `20' @ error/convert.c/ConvertImageCommand/3255.
This bug started in U18.04 initial release and still persists on latest U18.04 refresh - it has never been fixed.