In order for us to work with a plugin for an editor such as MSWord as mentioned in the previous post, we need to visit the object model exposed by that application. A word object model comprises of the following five top level objects:
Application object - represents the word application
Document object - represents the document and all of its content
Selection object - represents the area that is currently selected
Range object - represents a contiguous area in a document with a start and end character. It is active while the document is open and not visible.
Bookmark object - represents a contiguous area in a document with a start and end position and is persisted.
As you may see, they closely represent the hierarchy seen in the user interface.
At the top of this hierarchy is the application object. The application object contains document, selection, bookmark and range objects. Both the document object and the selection object can contain bookmark and Range objects.
Word also has content control objects. This let us control the input and the presentation of text and other types of content such as a date picker or a combo box. They help you do the following
prevent users from editing or deleting parts of document and
bind parts of a document or template to data.
One of the content controls is the Rich text. A rich text control contains text or other items such as tables, pictures or other controls.
A rich text content control has a DefaultTextStyle  and a PlaceholderText member. The former gets the name of the character style to format the text and the latter gets or sets the text that is displayed in the rich text content control.
A document also has XMLNodeControl to directly manipulate the markups and their hierarchy, This lets you define the xml content and schema that can be queried with XPath and displayed with content control objects. This is done by adding the custom xml part with the data from the xml and then binding the controls to custom xml part. XmlNodes can have a SmartTag object that represents the tag associated with the object.
The Range object can be used to format text in a Word document.
var start = this.Content.Start; // this.Sentences[0].Start
var end = this.Content.End;
Word.Range rng = this.Range(ref start, ref end); // this.Paragraphs[1].Range;
rng.Font.Size = 14;
rng.Font.Name = "Arial";
rng.ParagraphFormat.Alignment = Word.WdParagraphAlignment.wdAl
object indentStyle = "Normal Indent"
rng.set_Style(ref indentStyle);
rng.Select();
rng.Find.ClearFormatting();
rng.Find.Text = "find me";
rng.Replacement.ClearFormatting();
rng.Replacement.Text = "Found";
var replaceAll  = Word.wdReplace.wdReplaceAll;
rng.Find.Execute(ref findText, ref missing);