using System;
using Word = Microsoft.Office.Interop.Word;

class Program
{
    static void Main(string[] args)
    {
        Word.Application app = new Word.Application();
        Object fileName = @"D:\тест.docx";
        Object missing = Type.Missing;
        app.Documents.Open(ref fileName);
        Word.Find find = app.Selection.Find;
        find.Text = "<NAME>";
        find.Replacement.Text = "ТВОЙ ТЕКСТ ДЛЯ ВСТАВКИ";
        Object wrap = Word.WdFindWrap.wdFindContinue;
        Object replace = Word.WdReplace.wdReplaceAll;
        find.Execute(FindText: Type.Missing,
            MatchCase: false,
            MatchWholeWord: false,
            MatchWildcards: false,
            MatchSoundsLike: missing,
            MatchAllWordForms: false,
            Forward: true,
            Wrap: wrap,
            Format: false,
            ReplaceWith: missing, Replace: replace);
        app.ActiveDocument.Save();
        app.ActiveDocument.Close();
        app.Quit();
    }
}