The calculations are wrong, leading to single lines on a page. As a result, the content of the PDF document is laid out on a bigger number of pages.
Workaround: Change the line spacing and its type before exporting to PDF:
foreach (var paragraph in this.document.EnumerateChildrenOfType<Paragraph>())
{
HeightType? heightType = paragraph.Properties.LineSpacingType.GetActualValue();
if (heightType == HeightType.Exact || heightType == HeightType.AtLeast)
{
paragraph.Properties.LineSpacingType.LocalValue = Telerik.Windows.Documents.Flow.Model.Styles.HeightType.Auto;
paragraph.Properties.LineSpacing.LocalValue = 2;
}
}