Microsoft today released KB4100375 (OS Build 17133.73) to Windows Insiders running Build 17133 in the Fast, Slow, and Release Preview rings. This update does not include any new feature, but it includes the following bug fixes.

• Addresses a PDF security issue in Microsoft Edge.
• Addresses an issue that, in some instances, prevents Internet Explorer from identifying custom controls.
• Security updates to Internet Explorer, Microsoft Edge, Microsoft scripting engine, Windows kernel, Microsoft graphics component, Windows Server, Windows cryptography, and Windows datacenter networking.

With this update, Windows 10 RS4 RTM build number has now moved to 17133.73.

Source: Microsoft