Question: I was advised by users over on the Law Stack Exchange to ask this here:

I have created a piece of software that converts a proprietary format from the database blob of a large, well known commercial software company into the equivalent open source data type. The large commercial software company states the following on their copyright and trademarks page "This work is protected under United States copyright law and other international copyright treaties and conventions." and links to the DMCA.

I was able to create the software because most details of the format were published in a post on their support forums and the rest I reverse-engineered.

I now wish to open-source my software so others can use it. My question has two parts:

1. Can I open-source this at all without getting sued?
2. Can I refer to the trademarked product the file format came from in my software and documentation? (I'm assuming I can't use it in the name of my software)

I'm in the UK. The large software company is in the US.

Edit: The data in the database is user created GIS data, inputted via the commercial program, it's just stored in a way that makes exporting difficult.

Answer: 
Based upon your followup, I see no real legal issues other than those mentioned in my first post.

**Please remember that I am not a lawyer, and hold no liability for this**

My reasoning:

1. They are a reference to unique, non-copyrightable place references.
2. They are user generated, not generated by the makers of the software.
3. There are multiple uses for a point on a map, over and above the specific functionality of the software.
4. There are multiple GIS software packages- Providing a converter between them probably comes under interoperability.

If the company decides that they don't like what you are doing, the onus will be on you to prove that what you are doing is legal and above board, not the other way around. 

You'll need to think about how you might prove this, and if this looks like getting serious, I'd again urge you to get into touch with a lawyer, as the law is very easy to trip yourself up on.

You especially need to be wary of the differences between American law and British law- Whilst I know some about British law, I know nothing about American law.
If what is under said restrictions is the database blob, and they can make the case that the conversion "removes a copyright protection measure" (or however the law states it) you can certainly land in very hot water for encouraging or providing tools to do just that.