When we open a PDF in the browser from a document library, and then press the back button we get page expired.
One possible solution we have found is to open the PDF in adobe reader, as per this post.
Is their a way to solve this that does not involve changes to the registry on the client.
When you open the PDF inline in browser you get a "page expired" when you go back?
Where do you open the document from? Is it from inside a document library or from custom code?
I am asking this because getting a "page expired" is connected to doing a POST request (postback) and accessing from a document library is a GET request.
Caching can also be an issue, but again only in combination with a POST. You can examine what output cache profile you are using (an easy way to do this is by checking the Cache-Control header in the response header of the page using a program like Fiddler
