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: 
To be a little more precise on the above response:
Take two different scenarios as follows-
1. A database containing proprietary data which you cannot generate yourself.
2. A database generated from user inputs in your application.

If your database generally speaking conforms to #2 (Accounting software, sales etc.), then in the most general of terms you are likely to be able to do this.
How this will be received is another thing altogether- Many companies will aggressively attempt to shut you down, whether or not you are completely legal.
I also don't know exactly what was posted on their forums, or for that matter what the TOS of the forums was- If the TOS of the forums states that you cannot use data posted here to reverse-engineer etc. then you may have problems.

On the other hand, as the previous answer notes, if the contents of the database are what is proprietary, then you could *potentially* land in trouble.
Again though, this is by no means certain. It very much depends on the terms of the license agreement that you signed when installing the program initially.

This is probably one where you'll need to consult a lawyer, as I suspect there's a good chance that they may take of fence whether or not you are 100% legal, and being able to point them in the direction of a concrete legal opinion is far better than what you're going to get here.
Either way, we need far more details to be of any use to you!
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.