You can use 3rd party indicators within your strategies or custom indicators. A 3rd party indicator is an indicator that was not developed by NinjaTrader. It is important to understand from the 3rd party developer, the functionality provided or NOT provided in their proprietary indicators. Just because they provide an indicator that displays a bullish or bearish trend on a chart does NOT mean that you can access this trend state from their indicator.
3rd party indicators can be provided to you in one of the following ways:
If you were provided with a NinjaScript archive file that you have successfully imported via the Control Center window "File > Utilities > Import NinjaScript" menu you are can skip over the information below since NinjaTrader automatically configures the indicators ready for use.
If you were provided with a custom installer or a compiled assembly (.DLL) file that you had to manually save in the folder My Documents\<NinjaTrader Folder>\bin\Custom then you must follow the instructions below.
Vendor File
The 3rd party developer should have either installed a "Vendor" file or provided you with one. Its likely in the format "NinjaTrader.VendorName.cs" where VendorName is the name of the 3rd party vendor. This file allows you to conveniently access their indicators.
Adding a Reference
1. From within any NinjaScript indicator or strategy (Tools > Edit NinjaScript > Indicator and open any indicator in the NinjaScript Editor) , right click on your mouse to bring up the context menu and select the sub-menu "References..." as per the image below

2. A "References" window will appear
3. Press the "Add" button and select the 3rd party vendor DLL file

4. You will see a reference to the 3rd party vendor DLL in the "References" window
5. Press the "OK" button
You will now be able to access the indicator methods provided by the 3rd party vendor.