I am trying to shrink pdf files that are too big, using the colorsync filter from within DTP without having to export the file + use my automator process + reimport the file.
Is there any way do do it from within (services, etc.)?
Thanks a lot. These would save me a lot of time. 
It might be possible via ColorSync scripting (just a thought - I’ve never tried this).
Yes but can I use my Automator process which works well in th eFinder within DTP?
Should be possible. Here’s a possible approach:
[DTPro - Get Selected Records]
+
[DTPro - Get Data from Records: Get Path]
+
[insert your workflow here that needs as input files]
+
[DTPro - Set Current Group] Note: select a new group here, since it opens in a new window, your previous selection will be unchanged and you could remove those records if you want there once you verified that everything is ok. Then you can move the updated PDF records back after this workflow has ended and your verification.
+
[DTPro - Add Items to Current Group]
I hope that this will get you started. Note that you could drop this workflow in the Script Folder of DEVONthink Pro. Then it is always available from within the app.
It did not get me started as I could not get any action done on the selected pdf file!
I have tried multiple combinations of the Automator puzzle pieces witout success…
By default on import DT makes a copy of the file into the database. In that case the “Path” of a record will be empty.
This reminds me that I should create an “Export” action, this would solve the problem. 
As a temporary workaround you could move the records to a group and export the group to a folder (by hand using the File->Export…" menu). Then work on the resulting files.
This is exactly what I discovered myself and I found a workaround similar to the one you suggest . Looking forward to an “export” action which I will use also for other purposes.
In version 1.1 (currently in beta) you will find an “Export Record” action that can export a record to disk. It will not change the datatype, so a PDF will be exported only as a PDF.
Hopefully this will help you with your workflows.