Hi there, thanks for your question.
Generally, no user would ever need to open a DLL file as it's a system file used by Windows.
If you're a developer and need access to DLL files, the below link may help:
https://www.wikihow.com/Open-DLL-Files
Otherwise, if you're experiencing an error with a particular DLL file, please post a screenshot and I'll see what we can do to troubleshoot it.
Thanks!