How do I prevent TB to fetch the contents of PDFs when dragging 'n dropping from Devonthink

Q & A - getting started with Tinderbox
2

You could have the container’s $OnAdd action set the text to “”.

Or you could do the same thing with an agent.

Or, you could have the container’s $OnAdd action move $URL to a user attribute $DevonThinkURL while clearing $URL itself, thus preventing Tinderbox from importing the text.

Or you could just delete the text.