Is there a way to decompile a DLL? If not is there a way to open the file where someone would be able to "understand" what the compiled code meant?

This is an issue because I am developing a program that will be accessable to the internet. If the dll becomes compromised even so much as somone could remotly understand the methods that I am using I am out ALOT of money.

Thank you,
Andrew Durstewitz