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).
Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 1, one copy inherited from each parent, form one of the pairs. Chromosome 1 is the largest human chromosome, spanning about 249 million DNA building blocks (base pairs) and representing approximately 8 percent of the total DNA in cells.