I want PDF files in MOSS 2007 Publishing site document libraries to open in a new window. Is it possible to achieve this by creating a custom HttpHandler? I don't want to mess with a site definition for something as basic as this...
I have never tried a HttpHandler for that purpose, but it seems plausible.
If your document library only contains PDFs you can do some nifty things with the Data Form web part where you can show the PDF on the same page (using IFrames) as they click through items in the library.
I also have this requirement and discovered that if you have Adobe Reader installed as part of your SOE and are using this to open your PDFs then the problem is not on the server but the client.
Adobe Reader has an option called "Disable display of PDF in browser" that you need to change on your clients.
If you want to correct this then you will need to roll out this registry patch or MST change to your clients. The downside is that this will affect how PDFs are opened from all web sites, not just your SharePoint server. I don't think this can be changed per site, you could ask at Server Fault.