switched .php to .htm

[newreality]

Today, after some reluctance especially after seeing PR on my pages for the first time , I switched the .htacces file to read php on .htm pages, so I swithced the extensions over to .htm (I'm assuming .htm and .html are about the same)

Thing is, the pages all have the same content -- php per htm page

a) Should I make custom 404 error pages for each of the "lost" php pages?

b) Should I add content to the new .htms - say at add a paragraph or few sentences at the minimum, to avoid the duplicate content trap?

why i did this? after some research I've found that for my subject matter, while most engines index .php pages, results for .htm are still much better. Top ranking.php pages for my area are quite rare. Maybe some of the engines have concluded (however right) that these types of pages are easily constructed dynamically in great numbers -- the subject has to do with calendars and dates. Which may be an exception. Also I've discovered to achieve backlinks most sites prefer .htms over .php's and this is the main reason.

[seobook]

I think the lack of .php pages in the search results is more of a reflection of the fact that within your industry they are perhaps less common than .htm pages.

[dannysullivan]

Matt Cutts from Google was once on a panel of ours and joked that not only did file extension not matter to Google but that he had a friend who liked to name his files odd things, like .oof or .abc.

I've worked with sites ending in .htm, .asp, .php, .html and of course plenty of pages that simply ended in /. Our blog pages have no extensions at all -- they end in date-time, like 050103-002201. In all cases, pages have ranked just fine. If it's valid HTML, it's valid HTML when read, not based on what the extension says.

As for the logistics, I'd redirect from old to new permanently where you can. Otherwise, any error pages should come back with a common custom 404.

[newreality]

Would you still redirect if the only change is the extension
(duplicate content?) The filenames read the same other than the extension.

I have two simple redirects leading to the the new (htm) pages now.