what will open documents with the ending like .dar .sif?

Answer 1

https://dalma.dev.java.net/nonav/maven/container/dar.html
SIF is the file extension for the Setup installation files associated with Microsoft Windows NT, since its part of a mutli program which is all in code.
these 2 files are not really documents as such, more parts of programs and libarys, u need proberly need a decomplier to open this.

Answer 2

I'd suggest you check up:
http://filext.com/

File extensions galore...