https://learn.microsoft.com/en-us/dotnet/api/system.windows.documents.flowdocument?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
FlowDocument Class (System.Windows.Documents) | Microsoft Learn
Hosts and formats flow content with advanced document features, such as pagination and columns.
class systemwindowsdocumentsmicrosoftlearn