If the creator of the PDF "form" did not make it interactive by taking the additional step of adding form fields, there's not a lot you can do with Reader unless they enabled the Typewriter tool, which is probably unikely as well.
There are some non-Adobe PDF viewers that allow you to add text, such as FoxIt Reader. But this won't work if the document has security settings that prevent it.
So to summarize, Adobe Reader will work if the PDF contains form fields, or you can use it to add text if it has the necessary usage rights that allow the Typewriter tool to be enabled.
Some non-Adobe PDF viewers will let you add text, but not if security settings prevent it.