The Spacing Before property of the paragraph at the start of the page should not be respected if it is not the first one inside the current section.

Manually overriding the Spacing Before property would resolve the issue.

First Footer of a section overrides the First Footer of another section after the merge. After merging 'Parent' document (with a different First Footer which is empty) with 'Child' document (with explicitly set First Footer), the First Footer of 'Child' overrides the First Footer of 'Parent' after PDF export.

Workaround 1: Disable 'Child' document's 'HasDifferentFirstPageHeaderFooter' and clear its First Footer's value:

Telerik.Windows.Documents.Flow.Model.Section section = child.Sections.First();
section.HasDifferentFirstPageHeaderFooter = false;
section.Footers.First.Blocks.Clear();

parent.Sections.First().Footers.Add(HeaderFooterType.First);

Line spacing is not preserved when exporting RTF to HTML and the lines are exported with the default line spacing.

Updating a Table of Contents field with a custom TOC Style does not respect it.

As a workaround modify the style after the TOC fields are updated.

Similar to https://feedback.telerik.com/reporting/1356710-rendering-to-xlsx-should-not-add-bom-to-xml-files :

DOCX files exported with DocxFormatProvider contain a BOM in every exported XML file. Some programs fail to load those DOCX files.

Please remove the BOM, or add a toggle in DocxExportSettings.