I’ve done a search and unable to find the advantages of converting to RTF (which seems to create PDF+RTF copies) over simply PDF? Is this simply to allow editing (if so what are the behind the seen new then PDFs) and greater output control (assuming you can export either?)? I know PDFs can be searched also, so wondering if I’m missing other advantages?
If I don’t want PDF+RTF copies is there a way to go back to documents already imported and change, or do I need to reimport?
First, terminology. You have three choices for capturing text from PDF files using File > Import > Files & Folders (or dragging into DT Pro). Those conversion modes are specified in Preferences > PDF & PS.
Plain text. No images, no character formats.
Rich text (RTF). No images, but character formats (bold, italic) are retained.
PDF+text. Retains images, formats including layout for screen view.
All three modes of text capture and display use less memory than the file size of the original PDF file.
Index-imported PDFs result in capture of PDF+text, leaving the original file externally linked.
Personally, I prefer captures as PDF+text (you should be using Tiger to do this). The display is faithful to the original PDF document. If you need to copy selected text or even the entire text content, simply launch under Preview and select text, then copy it to the clipboard and paste it into a DT Pro document or a TextEdit document.
Yes, you can change the import modes for PDF, image and QuickTime files. Here’s how:
 From the top level view of your database, select all (Command-A).
 Select File > Export > Files & Folders to export all database content to a selected target folder (which should previously have been created in the Finder).
 Select File > New Database. Name the empty new database and save it to a desired location.
 Select DEVONthink Pro > Preferences and change the relevant import preferences. Example: change the conversion mode for PDFs from PDF+text to Rich text.
 Import the contents of your target folder containing the exported material into the new database, e.g. select File > Import > Files & Folders. Then select File > Database Properties and check to make this the new default database. Do not discard the target folder if your revised import procedure now results in external links to files in that folder. Example: If you had switched to File > Index to import the contents of the target folder, those contents would remain externally linked, and your database could not display them if the target folder were deleted.