50 US Pounds are equal to 22.69 Kilograms.
Cup Weight varies quite a bit depending on how one fills the cup with the flour. We wanted to set a standard here on the Forum but have not yet agreed upon that. I personally prefer weighted measurements for accuracy and consistency.
Assuming that a cup of flour filled flat contains:
4,0 oz (113,40 grams) then 12 grams Protein per cup would be ~ 10,6% Protein
4,5 oz (127,57 grams) then 12 grams Protein per cup would be ~ 9.5% Protein
5,0 oz (141,75 grams) then 12 grams Protein per cup would be ~ 8.5% Protein
As you see you probably have a bread flour with a not very good protein level. Does the maker of the flour specify the weight of the cup on the bag. If you ask me they probably didn't want to label the bag with the protein percentage to the total weight to mask up the true Protein content. The protein level in the flour you bought is more that of cake or pastry flour. It doesn't mean that the flour you bought is bad, it may perform good for Pan pizza, Chicago style or Thin Cracker Crust.
1% Vital Wheat Gluten (based on the weight of the flour) would raise the Protein content by 0,6%. So to raise the protein content of your flour by 1/2 percent, that would mean:
per 4,5 oz Cup (127,57 g) of flour plus 1% wheat gluten would mean you need to add 0,045 oz or 1,275 grams. Multiply accordingly to raise ever more.
High Gluten flour is needed for New York Style crust to create that "bite" and "Chew" typical to New York Pizza.
Maybe DKM, Steve or Randy can answer if they would use it for the other styles crusts as well.
If you are wanting to make a cracker thin crust you will probably want to roll out the dough thin. Many pizzerias use a mechanical sheeter for that, the rolling pin would be the cheapest homemaker version.