Thanks for your inquiry. Your expected document has left indentation for second and forth paragraph. Please use the ParagraphFormat.LeftIndent property to sets the value (in points) that represents the left indent for paragraph as shown in following code snippet.
Document doc = new Document(MyDir + "CURRENT.docx");
Paragraph para = (Paragraph)doc.GetChild(NodeType.Paragraph, 2, true);
para.ParagraphFormat.LeftIndent = 36;
doc.Save(MyDir + "out.docx");
Hope this answers your query. Please let us know if you have any more queries.