Today I went to clean out my cache files and when I clicked on them this popped up...(How do you want to open this file?). There were lots of options such as Wordpad, Notepad, Windows Media Player, etc. How do I get the file open? In the past they always just opened on their own.

Do you mean the following Cache files, found in your Sims 3 folder in Documents/Electronic Arts?

CASPartCache.package
compositorCache.package
scriptCache.package
simCompositorCache,package
socialCache.package

If so, may I ask why you are trying to open them? Usually, the advice to clean (or clear) them just means you need to delete them, not open them.

While I am positive this is not what the OP intended to do, we have had players attempt to open those cache files with various programs in the past to figure out how they work. That effort always led nowhere, even the contents of the files that never grow above 1 kb (so we assume it points somewhere else where the "real" caching is happening) remain a mystery.

But yes, the goal here is to delete the files in their entirety while the game is not running and thus allow them to respawn on the next game launch, not to open them up in a program to examine their contents.

Thank you everyone. I had temporary brain fog at the time because it had been awhile since I had deleted my cache files. Thanks for bringing me back to my sanity. lol