I have some code to replace text inside a word 2010 docx.
object fileName = Path.Combine(System.Windows.Forms.Application.StartupPath, \"document.doc
From Visual Studio 2013 you can do this:
Microsoft.Office.Interop.Word.Range range = this.Application.ActiveDocument.Content;
range.Find.ClearFormatting();
range.Find.Execute(FindText: "find text", ReplaceWith: "replace text", Replace: Word.WdReplace.wdReplaceAll);
(Posted for the benefit of anyone, like me, who came across this question but is not necessarily using the same versions of the tools as the OP.)