Microsoft .NET framework 3.5 can be installed on windows 10 without having installation media. The file you need is called microsoft-windows-netfx3-ondemand-package.cab
. Just google it and you will get the download links.
After downloading it, copy that file to C:\dotnet35
and run the following command.
Dism.exe /online /enable-feature /featurename:NetFX3 /All /Source:c:\dotnet35 /LimitAccess
Tested and worked in Windows 10 without any issue.