use find command in conjunction with string replacement

In bash, one can do something like this in a for loop to, say, convert pdf files in a directory to pngs systematically.

for file in $(ls .)
do
  convert ${file} ${file/.pdf/.png}
done

Note here that bash string replacement syntax allows for concise code.

When I tried the same with find I'm hopelessly stuck. Is there any way of implementing this with find in conjunction with (similar) string replacement syntax? Of course one can do this for example like this

find . | sed "s/\.pdf//" | xargs -i convert {}.pdf {}.png

but I like the idea of being able to use (something like bash) string replacement syntax together with find -exec

You have to run the shell.

find . -maxdepth 1 -exec bash -c 'convert "$1" "${1/.pdf/.png}"' -- {} \;

You can export a function for readability and correctness.

func() {
   convert "$1" "${1/.pdf/.png}"
}
export -f func
find . -maxdepth 1 -exec bash -c 'func "$@"' -- {} \;

Finally, you can use xargs to parallelize workflow.

func() {
   convert "$1" "${1/.pdf/.png}"
}
export -f func
find . -maxdepth 1 -print0 | xargs -P$(nproc) -0n1 bash -c 'func "$@"' --

Check your script with shellcheck.