What is the quickest way to convert Rich Text files within DTPO to .pdfs?
As a practical matter, I prefer keeping my notes, drafts and clippings from the Web as RTF(D) files. I can edit them, copy text to the clipboard without the artifact of hard line endings in PDF, and they take less storage space than PDF.
I’m not sure why you want to convert rich text to PDF, but here’s why and how I usually do that.
There are times when I want to send something to someone else who may not use a Mac, or to edit and polish a draft in a capable word processor and send the result out as PDF.
I created a Pages 09 template document with generic header and a footer that shows page number of x total pages.
I select the content of a rich text document, copy it to the clipboard and paste it into that Pages document that I’ve brought up from the template.
Why Pages 09? My graphics are properly placed, my hyperlinks all work and after customizing the generic header and perhaps adding footnotes I can export it as PDF (either to the Global Inbox, or to the Finder). I don’t even have to save it as a Pages document to produce the PDF. Looks good, prints well, cross-platform and takes only seconds to produce.
Any number of word processors can be used this way, but many of them require tinkering with images and/or hyperlinks, which is why I settled on Pages.
Oh my, what a reply! 
What about print to pdf?
take your rtf-document, press cmd+p, choose pdf, choose "save pdf to Devonthink.
You will find it in the global inbox …
That has never worked for me, that is, printing from within DT and saving the PDF back into DT.
I have the Global Inbox in the Finder’s Sidebar, and what does work for me is to print the PDF to disk and choose the Global Inbox as the destination.
Oh, Greg, you´re right, sorry.
I never tried this, but I thought it should work. Now I tried it, and it doesn’t.
I can´t find the pdf? Search in DTPO nothing, search with spotlight, nothing.
So, one have to save it to the desktop and then import it.
Yeah I tried print to pdf to DT and it doesn’t appear to work.
That’s right.
But notice that there are other options after you click the PDF button in the Print panel. For example, the option Save as PDF. The result will be a searchable PDF that can be saved to Inbox or elsewhere in the Finder.
But then you have no control of margins, page breaks, no page numbering and hyperlinks may not work – which is why I adopted the practice of clipping the rich text document into a template-generated word processing document. 