well, then you can only send it to your designer and ask him to rewrite the file in AI format.
Sorry but this board is meant for user-to-user support for Adobe Illustrator. If you're asked which vector editing software you are using (which seems quite obsolete) and the answer is that you don't have any than what do you expect the community to do for you? You can go for a walk to your gas station but when you ask them to check your brakes you will only receive a funny expression on the faces.
If you have a proper PDF (and let's hope there are no rasterized images embedded) you can try to open it directly in Illustrator and save it as .ai. In case there are gradients or any effects used in the PDF it's not going to work 100% but if there are only simple vectors it will do.
I don't think that many (if any) other vector editing software will open PDF to access the vectors inside.