We also publish to our own NuGet feed as a backup in addition to official nuget.org site and if you want to install from there, run this command:
Install-Package GleamTech.DocumentUltimate -Source https://get.gleamtech.com/nuget/default/
If you prefer using the user interface when working with NuGet, you can also install the package this way:
Add GleamTech's own NuGet feed first to be able to find GleamTech's packages. Go to Tools -> NuGet Package Manager -> Package Manager Settings and then click the + button to add a new package source. Enter GleamTech in Name field and https://get.gleamtech.com/nuget/default/ in Source field and click OK.
Go to Tools -> NuGet Package Manager -> Manage NuGet Packages for Solution, select GleamTech or All in the Package source dropdown on the top right. Now enter GleamTech.DocumentUltimate in the search field, and click Install button on the found package.