Have you tried qpdf? You can install it using Homebrew/MacPorts and run it via the Terminal. It is super easy to set up and use.
I’d give it a shot before using a web based utility given the privacy implications. This thread will be helpful if you are giving it a go. You can ignore the automation bit if that isn’t something you are looking to do but you can get a nifty workflow going if you add Hazel to the mix.