So, Microsoft don't provide a full offline installer for Office 2016, so here's how to make your own via legitimate means:

Create a "configuration.xml" file with the following:

<Configuration>
<Add OfficeClientEdition="32" >
<Product ID="StandardRetail">
<Language ID="en-us" />
</Product>
</Add>
<Display Level="Basic" AcceptEULA="TRUE" />
</Configuration>

Replace "StandardRetail" with one of:

StandardRetail
HomeBusinessRetail
HomeStudentRetail
ProRetail
ProPlusRetail

These represent the 5 non-365 editions of Office 2016.

Now, get the deployment "tool" from https://www.microsoft.com/en-us/download/details.aspx?id=49117

Run it, extract it somewhere and copy the .xml file to the same location.

Now, fire up a command shell, CD to the location of the files and run;

setup /download .\configuration.xml

It'll then download the entire (Approx 1GB) download media to an Office folder in the current location.

Now, to actually install the product, you would run;

setup /configure .\configuration.xml

The useful trick with this is that all 5 editions are included in the same cache, so by having 5 different XML files with the appropriate Product ID in each one, you can install any edition you like by providing the appropriate .xml on the commandline. I've created a .VBS that'll query which version to install. We do have a practical legitimate use for this.

You WILL obviously still need a valid license key and Microsoft account to be able to actually register and use the product, but if you need an offline installer for some purpose, then this will do the job.

The same trick also works with Office365 and the 4 editions of that, but you need the appropriate ProductID(s) and deployment tool.

The configuration.xml above will create an unattended passive installation, you can set the display level to "None" or "Full" as required. You can replace "32" with "64" if you need the 64-bit version as well.

The language MUST be "en-us", it doesn't recognise any other standard language ID's for English (so no "en-NZ")