Stronghold 3 is not very easy to modify at first glance. In fact, it's much harder then modifying crusader 2 and this is due to the fact that files are archived in a '.v' format. But whenever you attempt to open the file with an archiving program, such as 7-Zip you get the message that it cannot be opened as an archive. However, rest assured that all your problems are now solved. Using this modding tool, Stronghold 3 can now be modified like any previous game in the series. It does not require any installation; simply extract and run.
First off, ensure that Stronghold 3 is closed. It's not a good idea to mess around with the files while the game is open. Before we can actually begin, we must find where the files themselves are located. This does however, depend on where Steam is installed on your machine. The default directory is in Program Files on a 32-bit machine, or Program Files(x86) on a 64-bit machine.
You can find out which type of system you have by going to start -> Right Click on "This PC" or "Computer" -> Properties. However, I will show you an easier way. Go to the start menu, type 'Steam' in the search box, right click on it then select 'Open File Location'. From there go to:
SteamApps -> common -> Stronghold 3 -> assets
Now, find all of the '.v' files and place them into a different folder. This process has not proven to corrupt files, but it's always a good idea to have a backup of your files, in case the worst happens - especially since Stronghold 3 is not the most stable of games to begin with. These files include core.v, loc.v, update.v, update2.v and update3.v. From there, place the extracted program downloaded into the same folder. The next step is very important because it is one which the entire process depends on. Select the file you wish to unarchive, elect to rename it and change the extension to 'txt' (a text file). Windows will spit out an error saying the file extension will become unusable, just laugh and click on yes.
Note that in some versions of Windows, file extensions may not be shown automatically, meaning you can't edit the file extension - so when you are changing the name to .txt, it's part of the name you are adding instead of the extension (particularly newer versions of Windows). If this is the case, for Windows 7 or Vista, follow this guide. For Windows 8 or 10, use this one. You can now change the file extension.
Now left click on the chosen .v file, and drag it to the modding tool. Do not directly open the modding tool you downloaded, otherwise it will instantly close itself.
Depending on the file size, it can take a few seconds to make it readable. During this time, a command line window will appear, ensure that it's left alone, as it will close when ready. Once the process has completed, you will see a file with the exact same name in the directory, with the extension '.v'. This time, open it with a zipping program, such as WinRAR or the program I'm using is called 7-Zip. Now, you can open the file with the zipping program and see what is inside, allowing you to unarchive the contents and modify the game.
In order to add these files back into the game, compress them into a zip archive, and drag it to the modding tool once more. It will then make it compatible with the game and you can no longer edit or view the content.
If you have any trouble with this tutorial, please feel free to create a new topic in our Stronghold 3 forum.