@njsg @kasdeya Yup due to the double-slashes, correct one would be ${fname%.pdf}-crop.pdf (standard) or ${fname/%.pdf/-crop.pdf} if you really want to stick to bashisms.
See https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_06_02 for the standard specification.