The answer might depend upon what the recipient will do with the file.
If they're expecting a photo, which could (for example) be incorporated into a report, then sending the original jpeg from your camera would be the obvious thing to do; converting it a a pdf would be pointless and could make it harder for the recipient to make use of.
Similarly, if you're submitting an article to a magazine, the editor will probably want to to make changes to it, and then to copy and paste the article into the magazine. That's dead easy for the editor to do if you send it as a Word document but far harder if you send it as a (non-editable) pdf. Even so, if you were sending the article to the local vicar, for inclusion in the parish magazine, it might be best to ensure that you use the older .doc Word format, rather than the newer .docx one, in case he's only got an old version of Word on his computer.
If it's your c.v. that you're submitting to a potential employer, then Word format would be acceptable but pdf might be preferable in order to ensure that it's displayed on the recipient's screen inexactly the same way that it is on yours. That would be particularly important if you've used a non-standard font (that most people won't have on their computers) when preparing your document. Using pdf will see the font preserved but a Word format would see it replaced by something else on the recipient's screen.