Gimp 3.0.0 Already Has A Killer Plugin -> GUI Batch Image Conversion And Editing (including with PDFs)
Gimp 3.0.0 Already Has A Killer Plugin -> GUI Batch Image Conversion And Editing (including with PDFs)
GitHub - kamilburda/batcher: Batch Processing Plug-in for GIMP 3
Throw this python plugin into your GIMP 3.0.0 installation's plugin folder (if you already have gimp installed, uninstall it and make a fresh install, at least that is my advice).
When you open GIMP under "File" is the "Batch Convert" option, which brings up a really nice GUI for doing conversion of image files, but also basic edits.
I know there are command line utilities for this kind of thing, I know there are paid commercial programs that do this kind of thing.. but having an open source optional-GUI utility that does this that also happens to be attached to an extremely mature and fully featured open source image editor is pretty awesome.
Unfortunate that it's hosted on GitHub, but the software is FOSS. (BSD 3-Clause)