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As for your question, the line spacing is a parameter that specifies the spacing between lines in the same paragraph. Setting LineSpacing = 1 and LineSpacingType = Multiple (the default value) specifies that the line will be as high as 1 * the maximum word height in the line. That is why if you set it to a value less than 1, this will cause text to overlap and the selection will not show correctly.
If you want to set an exact value, say 15 pt, to be the line spacing, you could do so as follows:
e.Document.LineSpacingType = LineSpacingType.Exact;
e.Document.LineSpacing = Unit.PointToDip(15);
Again, if the height of the line is larger than 15 pt, the text will overlap.
Perhaps the property you are looking for is ParagraphDefaultSpacingAfter
, which has a default value of 9pt and is the space between adjacent paragraphs? This one can be set to 0 and will simply cause no spacing between paragraphs.
All the best,
the Telerik team