German umlauts (the characters 'Ä', 'Ö', 'Ü', 'ä', 'ö' and 'ü') will not be printed to a generated pdf file, but the other German "special" character "ß" works.

I use the trial version via the Telerik NuGet feed. A test program and my locally generated file are attached.

 Tables should ignore fixed proffered width with the value of 0, this is the default behavior in Word as well.

Workaround (when converting Flow to PDF documents): 

foreach (var item in tables)
{
    if (item.PreferredWidth.Type == Telerik.Windows.Documents.Flow.Model.Styles.TableWidthUnitType.Fixed && 
        item.PreferredWidth.Value == 0)
    {
        item.PreferredWidth = new Telerik.Windows.Documents.Flow.Model.Styles.TableWidthUnit(Telerik.Windows.Documents.Flow.Model.Styles.TableWidthUnitType.Percent, 100);
    } 
  
    
}

There is a wrong reference in the WPF .NET Core version of Telerik.Windows.Document.Fixed.dll that causes a FileLoadException with the message "Could not load file or assembly 'System.Drawing.Common, Version=5.0.0.0'"

Workaround: Add NuGet reference to System.Drawing.Common, version 5.0.0.0. Note: mark "Include prerelease" so you can see it in the NuGet Package Manager

A Link annotation must have an associated action, destination, or named destination specifying what should happen when the annotation is activated. When merging documents with invalid Link annotations, an ArgumentException is thrown with the message 'Value cannot be null. Parameter name: namedDestination'

Workaround: Remove the invalid annotations:

foreach (var annotation in document.Annotations.ToList())
{
    var link = annotation as Link;
    if (link != null && link.Action == null && link.Destination == null && link.NamedDestination == null)
    {
        (annotation.Parent as RadFixedPage).Annotations.Remove(annotation);
    }
}

Typically, it is the text to be displayed for the annotation or, if the annotation does not display text, an alternate description of the annotation’s contents in human-readable form.

This item will be closed as its subject is too broad. Please refer to the information below for the individual markup annotations.

As of now, the currently supported markup annotations are:

Text
Line
Highlight
Underline
Squiggly
StrikeOut
Stamp

The unsupported annotations and their respective feedback items are:

FreeText
Square
Circle
Polygon
PolyLine
Caret
Ink
FileAttachment
Sound