Depends on what kind of look you are interested in obtaining. If you like the distressed shabby look then chances are you can just clean the cabinets well, then paint over with latex- let it dry- take a sander to it to distress it and finish with a coat of walnut or ebony stain- wipe on /wipe off. If you want a traditional finish- smooth or bare wood- you need to take the doors off- and strip and sand. The cabinets frames (the part that you see) will also need sanded/stripped.
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Sometimes wood cabinets that have been painted can never be stripped back to the original wood- pits etc trap paint..
You can also faux them to look like stain.