Are all of the federal laws in the United States digitized and available to the public through some free ".gov" website? Is it possible to download them all into, say, PDF?
See http://uscode.house.gov/download/download.shtml to start.
But what exactly do you mean by a "law"? Lots falls under that term: do you include case law? SCOTUS decisions? Administrative policies? Read earlier Law SE question Naive approach to aggregating all US Federal Laws?
You may be interested in Cornell University's Legal Information Institute.
They have the US Constitution, the US Code, the Code of Federal Regulations, Supreme Court decisions, state laws, international law resources, and more, conveniently accessible from a single page.