How do I make a player unable to pick up certain tools?

I want to make it so that the player can only have one primary weapon, but I can't find any way to make a player unable to pick up a tool when they touch it. Edit: I have an idea. If I make it so that when the player is within a certain distance of a weapon and presses a button, it puts the tool in their backpack. The only problem is that i'm not sure how to find the magnitude between the player and any weapon pickup in particular that is dropped. Can someone help?

Put this local script in starter player!

While wait() do
        Local tools = script.Parent.Parent.Backpack:GetChildren()
        for i = 1, #tools do
             local tool = tools[i]
             tool:Destroy()
       end
end)

My capitalisations May be wrong cause I’m on a iPad! If you need anymore help ask.