using Spire.Doc;
using Spire.Doc.Documents;
using System.Drawing;
using System.IO;
using System.Text;

namespace CreateWordDocument_Doc
{
    class Program
    {
        static void Main(string[] args)
        {
            //實例化Document類的對象，并添加section和paragraph
            Document doc = new Document();
            Section section = doc.AddSection();
            Paragraph paragraph = section.AddParagraph();

            //讀取txt文件
            StreamReader sr = new StreamReader("test.txt", Encoding.Default);

            string line;
            while ((line = sr.ReadLine()) != null)
            {
                paragraph.AppendText(line);//在段落中寫入txt

                //設置段落樣式，并應用到段落
                ParagraphStyle style1 = new ParagraphStyle(doc);
                style1.Name = "titleStyle";
                style1.CharacterFormat.Bold = true;
                style1.CharacterFormat.TextColor = Color.Purple;
                style1.CharacterFormat.FontName = "宋體";
                style1.CharacterFormat.FontSize = 12;
                doc.Styles.Add(style1);
                paragraph.ApplyStyle("titleStyle");
            }
            
            //保存為docx格式的Word
            doc.SaveToFile("addTxttoWord.docx", FileFormat.Docx2013);
            System.Diagnostics.Process.Start("addTxttoWord.docx");

        }
    }
}

VB,NET

Imports Spire.Doc
Imports Spire.Doc.Documents
Imports System.Drawing
Imports System.IO
Imports System.Text

Namespace CreateWordDocument_Doc
    Class Program
        Private Shared Sub Main(args As String())
            '實例化Document類的對象，并添加section和paragraph
            Dim doc As New Document()
            Dim section As Section = doc.AddSection()
            Dim paragraph As Paragraph = section.AddParagraph()

            '讀取txt文件
            Dim sr As New StreamReader("test.txt", Encoding.[Default])

            Dim line As String
            While (InlineAssignHelper(line, sr.ReadLine())) IsNot Nothing
                paragraph.AppendText(line)
                '在段落中寫入txt
                '設置段落樣式，并應用到段落
                Dim style1 As New ParagraphStyle(doc)
                style1.Name = "titleStyle"
                style1.CharacterFormat.Bold = True
                style1.CharacterFormat.TextColor = Color.Purple
                style1.CharacterFormat.FontName = "宋體"
                style1.CharacterFormat.FontSize = 12
                doc.Styles.Add(style1)
                paragraph.ApplyStyle("titleStyle")
            End While

            '保存為docx格式的Word
            doc.SaveToFile("addTxttoWord.docx", FileFormat.Docx2013)
            System.Diagnostics.Process.Start("addTxttoWord.docx")

        End Sub
        Private Shared Function InlineAssignHelper(Of T)(ByRef target As T, value As T) As T
            target = value
            Return value
        End Function
    End Class
End Namespace

效果圖：