In some parts of the world people feel that because there is no visible money taken from the people who own software... that it is ok to use that software without paying for it.
As a professional programmer I can tell you how wrong that is. It is not yours and you can not use it without permission or payment.
If you decode the ExpressPCB file format and then make PCBs from your customers ExpressPCB files you have deprived ExpressPCB of income they have a right to. It is just as if you took the money out of their pocket.
If you provide such a converter to your customers you are enabling them to steal.
As a professional programmer I can tell you how wrong that is. It is not yours and you can not use it without permission or payment.
If you decode the ExpressPCB file format and then make PCBs from your customers ExpressPCB files you have deprived ExpressPCB of income they have a right to. It is just as if you took the money out of their pocket.
If you provide such a converter to your customers you are enabling them to steal.