I can't highlight and underline a text with my free version of adobe, how much is the full version?

I would suggest using the FoxIt Reader pdf program. The version I have is pretty recent, and allows you for free to highlight, add notes, etc, just like Adobe's paid version. Plus it starts up soooo much faster than Adobe Acrobate/Reader. The purchased version is pretty inexpensive too. I suggest you check it out.