Thank you both. I was just using that name merely as an example, although I did meet with him when I received my citizenship and he was a nice guy. His name is already out there on the internet so I doubt he would have a problem with my using it. In fact, the guy who I was writing yesterday's name is much different and it is HE who has the H. at the end of his name. Anyway - the letter is in the mail (so to speak).
If the other name you were wondering about had an “H.” at the end, then I agree with TG that it likely represents his maternal surname, so I would use the surname right before that. If you are responding in writing, you could use the whole name exactly as written (you mention the letter is in the mail). If spoken, it could be Sr. “paternal surname”, or “Don first name”. And yes, if any possible title, such as Licenciado or Doctor, use it.
When I first moved to Mexico, I had to use my mother's maiden name on many official documents, where I am Marsha Ostroff Cohen. When I mentioned that to my mother, she was very pleased to be a part of my official Mexican name!
Only in Mexico is my middle name on my documentation. In the States sometimes I had a middle initial.
My name is so UN-Mexican that if I am in a setting (say IMSS) where someone has something with my name on it and they want to shout it out to a group, they kind of stare at it for a bit and give up pronouncing it after my first name.
In the States I had my husband´s name and one name.. here 3 names and my father´s name, in France 3 names , my father´s name followed by spouse of my husband´s name.. makes it rough when I sign the debit cards .. have to remember where the card comes from..
Mexico is really picky about names and the US very laxed.. France on official papers is like Mexico.. picky..