You may get an error like this from Acrobat/Reader when you try to open a PDF in your browser:

Adobe Reader could not open ‘A9R3.tmp’ because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn’t correctly decoded).

On my server I have mod_deflate turned on and it compresses just about everything with gzip before sending it to the browser. This is what was causing the problem.

This issue shows up with IE6, but not IE7 or Firefox. It looks to me like the browser is supposed to decode/decompress the content before handing it to Acrobat. In the case of IE7 and Firefox the browser does it’s job correctly, but IE6 does not do this. Bad browser.

To work around this issue figure out what URLs can return a PDF file, then configure Apache not to use gzip when the request for one of those URLs came from IE6. In my case I just disabled gzip for the /jasperserver path and that did the trick. Of course you can use any rule that you can come up with, just set the variable “no-gzip”.

Here is what I used:

<Location /jasperserver>
BrowserMatch “MSIE 6.0″ no-gzip
</Location>