Open your document and click on the file menu, then click on Save As. On the right hand side you will need to choose a location to save the password protected version of the PDF. Now drop down the Save as type box and choose PDF. This will make an options button appear, click on it.
To do the math, each base pair takes 2 bits (you can use 00, 01, 10, and 11 for T, G, C and A). Multiply that by the number of base pairs in the human genome, and you get 2 * 3 billion = 6,000,000,000 bits. And remember, you have to go from bits to bytes to get to an answer in megabytes. A bit is just a single unit of digital information, but a byte is a sequence of bits (usually 8).
According to the Human Genome Project, there are between 26,000 and 40,000 genes in the human body. Each of these genes is composed of a unique sequence of pairs, each with four bases, called base pairs.