I have checked the import options of my version of ActivInspire (2.4) and i believe you are running the personal edition. You can check this by opening ActivInspire and clicking help and about, a box will open and in bold at the top if will give you the version you are running.
The import PDF open is locked to the professional version of ActivInspire you will need to purchase a license key to unlock this feature.
If you have Promethean hardware you can generate a license key for free, for instructions on how to do this please go to http://www.PrometheanKB.com and search for article 10937.
If you require any further assistance please do not hesitate to contact us.