Are you sure that the extension is .opd?
Check the extension again.
It is possible that you might have made a typo when you typed the subject of your original post which is
making other users think the file is something that is not.
If it is .odp, then it is most likely an OpenDocument Presentation.
http://www.filext.com/detaillist.php?extdetail=odp
OpenOffice.org, a free open source office suite, can view, open, create, edit, and save files in the
OpenDocument format is OpenOffice.org. At the time of this post, only OpenOffice.org 1.1.5 can open and view
files in the OpenDocument format. The new OpenOffice.org 2.0 can open, view, create, edit, and save files in
the OpenDocument format.
You find more information about OpenOffice.org at, well...
http://www.openoffice.org/
Download OpenOffice.org 1.1.5
http://download.openoffice.org/1.1.5/index.html
Download OpenOffice.org 2.0 RC1
http://download.openoffice.org/2.0.0rc/index.html
Other downloads can be found here:
http://download.openoffice.org/
And if you need a manual for OpenOffice.org (i.e. an installation manual), you can find them here:
http://documentation.openoffice.org/manuals/
To view PDF files, you need the Adobe Acrobat Reader. You can download it here:
http://www.adobe.com/products/acrobat/readstep2.html
To open an OpenDocument Presentation (.odp), first download and install OpenOffice.org.
If you are using OpenOffice.org 1.1.5, you will need to first start OpenOffice.org (from the Start Menu) and
click File -> Open...
OpenOffice.org 2.0 associates itself with OpenDocument files in Windows Explorer so that all you need to do is
double-click them to open. Alternatively, you could first start OpenOffice.org 2.0 (from the Start Menu) and
click File -> Open... to open the file.