A DLL is not usually a file you view it it used by a developer to send information needed to render a web page in a browser.
Here is a good link that explains the file format in detail.
It explains what company developed the file format,
its uses and what programs can work with this file format.
Once open in one of the programs listed you may be able to
save it in another format.
There are often additional programs and applications as well
but this is a starting point to try.
If you have further questions let us know.