Tech Trek – 2011.07.06
I was researching for methods to launch PowerPoint documents into slide show mode from a SharePoint document library. In SharePoint 2010, a document will launch into presentation mode once you save the file as “PowerPoint Show” format i.e. resulting into ppsx file extension.
Unfortunately, the side effect of this approach launches the dialog box below and prompts the user to confirm the operation for security reasons.
More interestingly, I’ve noticed that there is a feature with the new PowerPoint web viewer to start the slide show. By default, you will have to manually click a button when using the “View in Browser” option.
It caught my eye that there was a “PowerPointView=ReadingView” parameter being passed to the URL. After some research, I was able to find that there are a couple of options for this property. Viola! I was able to launch the slide show mode by replacing the value of the parameter into “SlideShowView” (camel-case required).
http://site/_layouts/PowerPoint.aspx?PowerPointView=SlideShowView&PresentationId=url
To that end, no dialog prompt was needed since the document was not opened using PowerPoint application. Unfortunately, launching this the first time will take time since it loads the viewer and the file into memory. Also, you will have to create such links manually, or may resort into creating custom menu actions to make it available to users.
MSDN resource: PowerPointView
Tech Trek Trenches (TIII) 
Hi,
Please elaborate how we can access the parameter being passed to the URL.
Thanks.
Jack,
You will have to manually create a link within a SharePoint page using the following syntax:
http:///_layouts/PowerPoint.aspx?PowerPointView=SlideShowView&PresentationId=url
I would suggest using the “View in Browser” option from the item dropdown and try replacing it from the browser URL. Just make sure that “SlideShowView” is written as shown since it is case-sensitive.