Smaj- the NFA was the law from the 1930s that required the payment of a transfer tax on machine guns (referred to here as FA for full auto) short barreled shotguns, suppressors, etc etc. Your PDF addresses making NFA firearms. Those are NOT ordinary rifles, handguns, and shotguns.
If you want to take a 20 lb chunk of steel and a pocket knife, and whittle yerself a .45 caliber pistol, it is legal to do that. It cannot be a full auto, and if you wanted to make a snubby shotgun, snubby rifle, a disguised firearm (cane gun, perhaps), a 40mm cannon or a suppressor, you will need to do the NFA paperwork and pay fees for those up front, THEN build.
If you are "engaged in the business" of making guns for sale, THEN you need a license as a manufacturer. Want to make the ultimate accurate .22 target rifle? Have at it.