If you have a MATLAB R2009b installation, documentation should be installed.
If you do not have the installation, but you have active software maintannce, you can install the product and the documentation (not documentation only) or access the onlince documentation.
If your license is out of maintenance before R2009b, you cannot access the documentation. It now depends on the reason why you need it. If you e.g. consider purchasing an upgrade, MathWorks Sales could provide you with a trial.