The file extension .WD3 , what it contain

i got a file in .WD3 extension ,  many questions in my mind

i noticed there`s a file "Descr.WD3" in each folder....
what is this file and how can i view his content?

or should i delete it??
So at last find an answer

Descr.wd3 files reside in each directory Offline Explorer creates and contain information regarding all downloaded files in the directory:
- file name
- original file URL
- date of the last modification on Web server (to check for updates)
- file MIME type as it was returned by Web server (this is useful for offline browsing)
- a sign, if a .primary file was created or not.

Although all these files could be deleted, it is not recommended because this may make Web site updates and offline browsing less reliable.