https://github.com/OfficeDev/Word-Add-in-DocumentAssembly
I am trying to implement functionality like the above link targeting office 2013, yet the source does not run correctly because of the lack of a 'Word' object in JS. Can this code be ported or is there an example of similar code targeting 2013?
The Word object is not available in Word 2013. You can implement much of the same functionality in Word 2013 by using OOXML and the different setSelectedDataAsync options. It won't be as convenient as what you have available in Word 2016. Here are some code samples that you can look through for examples. The older ones may have useful examples for your scenario.