I suppose I'll do a write-up on how to get a downloaded world into CAW, because I've found the following to be a pretty sure-fire recipe. It's not that difficult after all, but there are a few caveats, and there are some critical steps which you must do exactly right or it will fail.
First of, you need to download CAW, you must have your game fully patched, you need S3PE (preferably the x64 version) and you should have a 24-bit 256x256 .png file ready. That latter can be tricky but you can find some premade ones through here: http://forum.thesims...61.page#3736582. Since the EA forums may be a bit AWOL at times, I've also attached a sample to this post.
You should really rename your normal The Sims 3 folder, and let the game create a new one, without any mods or CC. The CAW tool has a folder of itself, The Sims 3 Create A World Tool, which behaves much in the same way in that it will be freshly recreated if the tool can't find it. This can come in handy.
1) Install the world in the usual way in your fresh game folder. If it is a real prerequisite, in that Riverview objects are used in the world, you'll need to install Riverview too. Of course this also goes for Barnacle Bay or any other custom world EA may release separately. This is also a good time to check in your Installed Items whether any "foreign" CC came with it.
2) Start CAW and make a new world. It will ask for a .png, press the ... box and you'll get a few 'starters', choose any. Accept all the rest and OK. You don't need to worry about parameters for your world as they will be overwritten later anyway. Save As the new world with a name you will use temporarily, not the definitive name you want to give it. Let's call it Temp.world for now. Close CAW.
3) Open S3PE and browse to the The Sims 3 Create A World Tool\UserToolData\Worlds and you'll find your Temp.world file. Open it.
4) Use Resource->Import->From package... and browse to your The Sims 3\InstalledWorlds and open the world file you want to "import". Accept the default settings for Import, when it asks you to save between packages, say No. It will show a progress bar so you'll know it's done. This may take a while.
5) Sort the resources by Type (click the "header") and find UNKN 0x296A6258 there. If all is well you should have two, one already deleted (struck out), right-click the other and select "Deleted" to delete it too. At the bottom of the file you should have two WPID resources, one already deleted, delete the other too.
6) Use the "close" button in the upper right to close S3PE. It will tell you the package has changed, choose Yes to save the changes. The reason for doing it this way is you'll know it's done when the S3PE window closes. This may take a while.
7) Start the CAW tool and open your Temp.world. Wait until the render window shows you a reasonable picture of something in the world. This may take a while and there is no real progress indication.
8) Right-click on the Temp.world on the left pane (World Layers) and choose Add/Edit description. Make sure the Name and Description fields are filled in. You can use your final name and description here. Also make sure there is a .png for the thumbnail. If there isn't, browse up one of the samples you got earlier or make sure you have one ready. This needs to be in the 24-bit 256x256 format!
9) Save As the world with the final name, let's say Final.world. It will give you a "wait" cursor for a while and then a normal cursor. Don't touch it!! It's not done! Leave the computer to it until a window pops up informing you the world is successfully saved.
Actually you've already done it now and you can delete the temp.world and the folder that belongs to it.
If you want to use Edit in Game, be advised that when you're done you need to save, this can take a LONG time and your screen will darken while each lot is saved separately. DO NOT Alt-Tab at this stage to do something else or the save will fail. Just don't touch the computer until the "Succesfully saved" list is displayed.
The opposite direction is quite simple, just start CAW and use "Export world". It will put a <your world>.sims3pack in your The Sims 3\Exports folder. You can take that out and put it in the Download folder and install it as usual.
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