PM> Install-Package Spire.PDF

using Spire.Pdf;
using Spire.Pdf.AutomaticFields;
using Spire.Pdf.Graphics;
using System.Drawing;


namespace AddPageNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            //初始化 PdfDocument 类的实例
            PdfDocument pdf = new PdfDocument();

            //加载示例文档
            pdf.LoadFromFile("示例文档.pdf");

            //设置页码字体样式
            PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("宋体", 10f, FontStyle.Regular), true);

            //初始化 PdfPageNumberField 类的实例
            PdfPageNumberField pageNumber = new PdfPageNumberField();

            //初始化PdfPageCountField 类的实例
            PdfPageCountField pageCount = new PdfPageCountField();

            //初始化PdfCompositeField 类的实例
            PdfCompositeField compositeField = new PdfCompositeField(font, PdfBrushes.Black, "第{0}页，共{1}页", pageNumber, pageCount);
            //设置复合字段的文本对齐方式
            compositeField.StringFormat = new PdfStringFormat(PdfTextAlignment.Left, PdfVerticalAlignment.Top);

            //循环遍历页面
            for (int i = 0; i < pdf.Pages.Count; i++)
            {
                //在页面的特定位置绘制复合字段
                compositeField.Draw(pdf.Pages[i].Canvas, pdf.Pages[i].Size.Width / 4 - 20, pdf.Pages[i].Size.Height / 2- 20);
            }

            //保存结果文档
            pdf.SaveToFile("添加页码.pdf");
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.AutomaticFields
Imports Spire.Pdf.Graphics

Namespace AddPageNumbers
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            '初始化 PdfDocument 类的实例
            Dim pdf As PdfDocument = New PdfDocument()

            '加载示例文档
            pdf.LoadFromFile("示例文档.pdf")

            '设置页码字体样式
            Dim font As PdfTrueTypeFont = New PdfTrueTypeFont(New Font("宋体", 10F, FontStyle.Regular), True)

            '初始化 PdfPageNumberField 类的实例
            Dim pageNumber As PdfPageNumberField = New PdfPageNumberField()

            '初始化PdfPageCountField 类的实例
            Dim pageCount As PdfPageCountField = New PdfPageCountField()

            '初始化PdfCompositeField 类的实例
            Dim compositeField As PdfCompositeField = New PdfCompositeField(font, PdfBrushes.Black, "第{0}页，共{1}页", pageNumber, pageCount)
            '设置复合字段的文本对齐方式
            compositeField.StringFormat = New PdfStringFormat(PdfTextAlignment.Left, PdfVerticalAlignment.Top)

            '循环遍历页面
            For i As Integer = 0 To pdf.Pages.Count - 1
                '在页面的特定位置绘制复合字段
                compositeField.Draw(pdf.Pages(i).Canvas, pdf.Pages(i).Size.Width / 4 - 20, pdf.Pages(i).Size.Height / 2 - 20)
            Next

            '保存结果文档
            pdf.SaveToFile("添加页码.pdf")
        End Sub
    End Class
End Namespace