What version of CorelDraw is this? Older versions have two PDF import filters and you could be using the wrong one for the purpose.
One of them just pastes the import into the file as a single object, which you can enlarge and reduce but not break apart into individual components. This in version 9 is called "PDF -- placeable enhanced PDF page" and is NOT the import filter you need for this purpose.
In v9, look instead for one named "PDF -- Adobe Portable Document File". This tries to identify the individual shapes and text within the PDF and create corresponding Corel objects for them. It will say something like "group of 8 objects". This is the import filter that you need, in order to ungroup and select objects individually.
However, its also possible that the PDF itself contains only a single object -- possibly a bit image. In that case, even using the second fiter, there will be no way to get anything out other than a bitmap. You may need to go back to your author and ask if they have it in vector form.