Do you have to reformat an SD Card before you can copy its contents to your PC?
No, you MUST NOT reformat it before copying! Formatting a storage device means to prepare it to hold files, and it will delete everything on it (see the tag wiki of the formatting tag for details). So yes, formatting woul imply losing all contents on the formatted device (in this case, from your SDCard).

New cards usually come pre-formatted, so there's no action needed either: Simply insert and enjoy. I never heard a device prompting you to format a newly inserted card, and I've had some of them. Of course, a warning is issued when you manually select to format a card, so you do not accidentally fall into such a trap.