(Texas) Grandmother passed away, left a handgun to my little brother(22) can't find any paperwork on the weapon

My grandmother passed away and before she passed she told my brother he could have her handgun. No one in the family has an issue with him owning it, but we cannot find any paperwork on it in her possessions, I'm not certain it is a good idea for my brother to keep the weapon in his possession with out any papers for it stating it's legality. How would we go about getting replacements for the weapon to show it was obtained legally?

Edit: Thanks all for the input, I'm not much of a firearms person!