Recently I was trying to add a Windows Feature into a Windows.wim file. 

After mounting the Wim I ran the below on a server 2012 machine

Dism /Image:”c:\temp” /Enable-Feature /FeatureName:NetFx3 /all

However I got 

Error 87 : “enable-feature is unknown”

I had to run the Dism /Image:”c:\temp” /Enable-Feature /FeatureName:NetFx3 /all command on a Windows 10 Box