Example:

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

// Below are three line spacing rules that we can define using the
// paragraph's "LineSpacingRule" property to configure spacing between paragraphs.
// 1 -  Set a minimum amount of spacing.
// This will give vertical padding to lines of text of any size
// that is too small to maintain the minimum line-height.
builder.getParagraphFormat().setLineSpacingRule(LineSpacingRule.AT_LEAST);
builder.getParagraphFormat().setLineSpacing(20.0);

builder.writeln("Minimum line spacing of 20.");
builder.writeln("Minimum line spacing of 20.");

// 2 -  Set exact spacing.
// Using font sizes that are too large for the spacing will truncate the text.
builder.getParagraphFormat().setLineSpacingRule(LineSpacingRule.EXACTLY);
builder.getParagraphFormat().setLineSpacing(5.0);

builder.writeln("Line spacing of exactly 5.");
builder.writeln("Line spacing of exactly 5.");

// 3 -  Set spacing as a multiple of default line spacing, which is 12 points by default.
// This kind of spacing will scale to different font sizes.
builder.getParagraphFormat().setLineSpacingRule(LineSpacingRule.MULTIPLE);
builder.getParagraphFormat().setLineSpacing(18.0);

builder.writeln("Line spacing of 1.5 default lines.");
builder.writeln("Line spacing of 1.5 default lines.");

doc.save(getArtifactsDir() + "ParagraphFormat.LineSpacing.docx");