Politely asked for a raise in a letter sent to my boss, boss was displeased

I've worked at a company for about 3 years and I decided it was time to ask my employer for a raise. Previously, I had asked upper management what the proper way to ask for a raise was at this company. The message I got was that employees don't typically discuss compensation with their managers because management tries to (and often does) do their best to be compensation leaders in the market. So the message was, you shouldn't really have much reason to discuss it.
Using this understanding, I thought that since having compensation discussions isn't the norm (which I don't really believe anyway), the best way for me to approach this topic is to just write a quick formal letter to my boss indicating what I felt a fair market value was for my position. I made sure to express appreciation for all my boss has done and that I genuinely enjoy working for the company. I listed all of the accomplishments I made this year and the ways in which I've contributed positively.
I pinged my boss on slack letting him know I'd be sending him a quick letter through email, but that I didn't necessarily need or expect a response. Just that it was more for his own information. I sent the letter, and after he read it he asked to do a zoom call with me.
In the call, he basically said that he thought I should have spoke with him first before sending a formal letter to him, and that it might be hurtful to our working relationship if I approach topics like this by sending formal letters. He also said I should have sent the letter through a password protected PDF because now my discussion of compensation figures could be potentially read by anyone.
I explained to him my previous reasoning that:

1. Previous compensation letters addressed to me were written in unencrypted PDF documents sent through email so I thought that was okay to do and
2. I had previously asked upper management (his boss) how to approach compensation discussions, and was basically told that employees don't really have the conversation at all, because management tries to give us fair salaries anyway. So using that understand I thought I would just not have a discussion, but send a quick letter instead. That way he'd know what my expectations were, but we didn't have to dive too deep into it.

Does anyone think I approached this the wrong way? Could I have done something better? I do see his point that maybe I should have spoken with him first. But I thought compensation letters are fairly standard and didn't think it would be an issue. I'm just questioning my judgement, maybe I need to seriously re-think the way I approach professional relationships like this. Any advice would be appreciated :(
tl;dr
I sent a letter to my boss asking for a raise. Boss was unhappy that I sent a letter and told me I should have just talked to him one-on-one first, because now there's a paper trail. Explained that I thought a letter would be the best way to go, based off my conversations with upper management. I just want to know if what I did was unreasonable, unprofessional, or if I had poor judgement with this situation. I feel frustrated because I felt like I did something wrong.


Source.