If you have a Mac, you can use Printopia. You get the option to send it to the DropBox folder on the Mac, to any printer connected to that Mac, and to the Mac itself (which opens the file on the Mac in Preview).
Since AirPrint outputs as PDF, that's what you get with both the non-printing options.
There might be a Windows equivalent, but I don't know it's name.
Also, you can get a DropBox email address to send files to at sendtodropbox.com, which should work with any app that will export and mail as a pdf.