Hi Waghmare,

Refer below sample.

Namespaces

C#

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

VB.Net

Imports System.Data
Imports Word = Microsoft.Office.Interop.Word

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[5] {
        new DataColumn("LastName"), new DataColumn("FatherName"), new DataColumn("Adress"), new DataColumn("Name"), new DataColumn("Birthday") });
    dt.Rows.Add("Pulodov", "Abdulloevich", "city Dushanbe", "Rustam", "22.12.1987");
    if (dt.Rows.Count > 0)
    {
        object fileName = Server.MapPath("~/Files/Test.docx");
        Word.Application word = new Word.Application();
        Word.Document doc = new Word.Document();
        object missing = System.Type.Missing;
        try
        {
            doc = word.Documents.Open(ref fileName, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing,
                ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
            doc.Activate();
            foreach (Microsoft.Office.Interop.Word.Range docRange in doc.Words)
            {
                if (docRange.Text.Trim() == "#")
                {
                    docRange.Text = docRange.Text.Replace("#", "");
                }
                else if (docRange.Text.Trim() == "Ln")
                {
                    docRange.Text = docRange.Text.Replace("Ln", dt.Rows[0]["LastName"].ToString());
                }
                else if (docRange.Text.Trim() == "Fn")
                {
                    docRange.Text = docRange.Text.Replace("Fn", dt.Rows[0]["FatherName"].ToString());
                }
                else if (docRange.Text.Trim() == "Ad")
                {
                    docRange.Text = docRange.Text.Replace("Ad", dt.Rows[0]["Adress"].ToString());
                }
                else if (docRange.Text.Trim() == "Nm")
                {
                    docRange.Text = docRange.Text.Replace("Nm", dt.Rows[0]["Name"].ToString());
                }
                else if (docRange.Text.Trim() == "Bth")
                {
                    docRange.Text = docRange.Text.Replace("Bth", dt.Rows[0]["Birthday"].ToString());
                }
            }
            object format = Microsoft.Office.Interop.Word.WdSaveFormat.wdFormatPDF;
            object destination = @"D:\PdfFile.pdf";
            word.ActiveDocument.SaveAs(ref destination, ref format, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing,
                                        ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        finally
        {
            doc.Close(ref missing, ref missing, ref missing);
            ((Word._Application)word).Quit();
        }
    }
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Dim dt As New DataTable()
    dt.Columns.AddRange(New DataColumn(4) {
                        New DataColumn("LastName"), New DataColumn("FatherName"), New DataColumn("Adress"), New DataColumn("Name"), New DataColumn("Birthday")})
    dt.Rows.Add("Pulodov", "Abdulloevich", "city Dushanbe", "Rustam", "22.12.1987")
    If dt.Rows.Count > 0 Then
        Dim fileName As Object = Server.MapPath("~/Files/Test.doc")
        Dim word As New Word.Application()
        Dim doc As New Word.Document()
        Dim missing As Object = System.Type.Missing
        Try
            doc = word.Documents.Open(fileName, missing, missing, missing, missing, missing,
                missing, missing, missing, missing, missing, missing, missing, missing, missing, missing)
            doc.Activate()
            For Each docRange As Microsoft.Office.Interop.Word.Range In doc.Words
                If docRange.Text.Trim() = "#" Then
                    docRange.Text = docRange.Text.Replace("#", "")
                ElseIf docRange.Text.Trim() = "Ln" Then
                    docRange.Text = docRange.Text.Replace("Ln", dt.Rows(0)("LastName").ToString())
                ElseIf docRange.Text.Trim() = "Fn" Then
                    docRange.Text = docRange.Text.Replace("Fn", dt.Rows(0)("FatherName").ToString())
                ElseIf docRange.Text.Trim() = "Ad" Then
                    docRange.Text = docRange.Text.Replace("Ad", dt.Rows(0)("Adress").ToString())
                ElseIf docRange.Text.Trim() = "Nm" Then
                    docRange.Text = docRange.Text.Replace("Nm", dt.Rows(0)("Name").ToString())
                ElseIf docRange.Text.Trim() = "Bth" Then
                    docRange.Text = docRange.Text.Replace("Bth", dt.Rows(0)("Birthday").ToString())
                End If
            Next
            Dim format As Object = Microsoft.Office.Interop.Word.WdSaveFormat.wdFormatPDF
            Dim destination As Object = "D:\PdfFile.pdf"
            doc.ActiveDocument.SaveAs(destination, format, missing, missing, missing, missing, missing, missing,
                                                missing, missing, missing, missing, missing, missing, missing, missing)
        Catch ex As Exception
            Response.Write(ex.Message)
        Finally
            doc.Close(missing, missing, missing)
            DirectCast(word, Word._Application).Quit()
        End Try
    End If
End Sub

The Word file and generated PDF