Recently, we had a customer expressing a desire to have black-and-white PDFs. Our head developer, Christian Grunenberg, suggested running a Quartz filter on them. When you export out of Apple’s Preview, you have the option of applying a Quartz filter to adjust the output. (A Quartz filter is a macOS filter for processing PDFs. You can see and try your hand at them in the Filters section of /Applications/Utilities/ColorSync Utility.)
But you can also run Quartz filters on PDFs right inside of DEVONthink by using Automator. Inside of DEVONthink Pro or Pro Office choose Scripts > More Scripts and install the script Convert PDF to Grey. Then select one or more PDFs and activate the script (actually a workflow) with Scripts > Convert > Convert PDF to Grey. We suggest to run it not on hundreds of documents in one shot, though it’s up to you to make that decision). Also, note it does not preserve a copy of the file. It will directly adjust the file itself.
Feel free to choose Scripts > Open Scripts Folder and find the workflow in the Convert subfolder. Open it up, see what’s inside (it’s very simple), and even set the filter to a single choice instead of having to choose each time you run it. Hopefully, it will inspire you to look at other ways you can expand your DEVONthink experience!