Added InsertHorizontalLine as per vodamihai submit. Added some example code for usage scenario. Cleaned up examples a bit.

DocX/Paragraph.cs

             return this;
         }
 
+
+        public void InsertHorizontalLine(string lineType = "single", int size = 6, int space = 1, string color = "auto")
+        {
+            var pPr = this.GetOrCreate_pPr();
+            var border = pPr.Element(XName.Get("pBdr", DocX.w.NamespaceName));
+            if (border == null)
+            {
+                pPr.Add(new XElement(XName.Get("pBdr", DocX.w.NamespaceName)));
+                border = pPr.Element(XName.Get("pBdr", DocX.w.NamespaceName));
+                border.Add(new XElement(XName.Get("bottom", DocX.w.NamespaceName)));
+                var bottom = border.Element(XName.Get("bottom", DocX.w.NamespaceName));
+                bottom.SetAttributeValue(XName.Get("val", DocX.w.NamespaceName), lineType);
+                bottom.SetAttributeValue(XName.Get("sz", DocX.w.NamespaceName), size.ToString());
+                bottom.SetAttributeValue(XName.Get("space", DocX.w.NamespaceName), space.ToString());
+                bottom.SetAttributeValue(XName.Get("color", DocX.w.NamespaceName), color);
+            }
+        }
+
         /// <summary>
         /// Append a hyperlink to a Paragraph.
         /// </summary>

Examples/Examples.csproj

   </ItemGroup>
   <ItemGroup>
     <None Include="app.config" />
-    <None Include="DocumentWithBookmarks.docx">
+    <None Include="docs\DocumentWithBookmarks.docx">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
-    <None Include="DocumentWithTemplateTable.docx">
+    <None Include="docs\DocumentWithTemplateTable.docx">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
-    <None Include="Input.docx">
+    <None Include="docs\Input.docx">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
   </ItemGroup>

Examples/Program.cs

             HelloWorldAdvancedFormatting();
             HelloWorldProtectedDocument();
             HelloWorldAddPictureToWord();
+            HelloWorldInsertHorizontalLine();
             RightToLeft();
             Indentation();
             HeadersAndFooters();
         {
             Console.WriteLine("\tCreateTableFromTemplate()");
 
-            using (DocX docX = DocX.Load("DocumentWithTemplateTable.docx"))
+            using (DocX docX = DocX.Load(@"docs\DocumentWithTemplateTable.docx"))
             {
                 //look for one specific table here
                 Table orderTable = docX.Tables.First(t => t.TableCaption == "ORDER_TABLE");
         {
             Console.WriteLine("\tBookmarksReplaceTextOfBookmarkKeepingFormat()");
 
-            using (DocX docX = DocX.Load("DocumentWithBookmarks.docx"))
+            using (DocX docX = DocX.Load(@"docs\DocumentWithBookmarks.docx"))
             {
                 foreach (Bookmark bookmark in docX.Bookmarks)
                     Console.WriteLine("\t\tFound bookmark {0}", bookmark.Name);
             }
         }
 
+        static void HelloWorldInsertHorizontalLine()
+        {
+            Console.WriteLine("\tHelloWorldInsertHorizontalLine()");
+
+            // Create a new document.
+            using (DocX document = DocX.Create(@"docs\HelloWorldInsertHorizontalLine.docx"))
+            {
+                // Insert a Paragraph into this document.
+                Paragraph p = document.InsertParagraph();
+
+                // Append some text and add formatting.
+                p.Append("Hello World!^011Hello World!")
+                .Font(new FontFamily("Times New Roman"))
+                .FontSize(32)
+                .Color(Color.Blue)
+                .Bold();
+                p.InsertHorizontalLine("double", 6, 1, "auto");
+
+                Paragraph p1 = document.InsertParagraph();
+                p1.InsertHorizontalLine("double", 6, 1, "red");
+                Paragraph p2 = document.InsertParagraph();
+                p2.InsertHorizontalLine("single", 6, 1, "red");
+                Paragraph p3 = document.InsertParagraph();
+                p3.InsertHorizontalLine("triple", 6, 1, "blue");
+                Paragraph p4 = document.InsertParagraph();
+                p4.InsertHorizontalLine("double", 3, 10, "red");
+
+
+                // Save this document to disk.
+                document.Save();
+                Console.WriteLine("\tCreated: docs\\HelloWorldInsertHorizontalLine.docx\n");
+            }
+        }
+
         static void HelloWorldProtectedDocument()
         {
             Console.WriteLine("\tHelloWorldPasswordProtected()");
             const string str = "Hello World";
 
             // Open the document Input.docx.
-            using (DocX document = DocX.Load(@"Input.docx"))
+            using (DocX document = DocX.Load(@"docs\Input.docx"))
             {
                 // Make sure this document has at least one Image.
                 if (document.Images.Count() > 0)