Matches have to be recorded so here is a simple discription how to do it.

The command is:
/record desireddemoname

You also can use:
/record
(without a certain name) Then the demos will be named with: demoXXXX.

If you record you will find "RECORDING demoname: filesize" in the left bottom margin.
An example you can find here:
http://download.esl.eu/matchmedia/87710 ... 018228.jpg

Your record will be in the gamefolder under C:\...\Activision\Call of Duty 4 - Modern Warfare\Mods\pam4\demos

The filename will be: desireddemoname.dm_1 or demo000.dm_1 (depending on your entrys you made before)