Sorry this topic goes a little afield from Devonthink, itself, but it does address a roadblock to lessening PDF file sizes. Other threads have suggested using an automator action (compress images in pdf documents) or using the action “Apply Quartz Filter to PDF Documents” w/ the Reduce File Size Options.
I’ve tried both without success and hoped someone could lessen my ignorance.
I set up an automator application with only the Compress Images in PDF Documents action. When I drag a file onto it, whether from DTPO or from the Finder, the application starts and quits but the file is unchanged.
Then, I tried to setup the Apply Quartz Filter to PDF Documents action but all the options were grayed out in the filters.
Any advice on navigating this? Thanks! 
This isn’t a response to how to set up automated compression, but may be useful. See the link for directions on how to create a custom Quartz filter. meyerweb.com/eric/thoughts/2010/ … -x/#jmp0
Thanks for the lead Bill. I did download and place the file as the link suggested. It worked beautifully. Thank you. I’d like to automate the reduction so that the old file is trashed and replaced with the new, reduced file. I’ll work on that. In part, I figure I can use at least that filter in Automator to create a workflow or app.
Interestingly, when I open the Colorsync Utility, only the downloaded filter shows available options. The options on all the other filters are still grayed out. And, I noticed that the folder where the filter was placed was otherwise empty.