PDF 圖層是一種將 PDF 文件的內容按圖層排列的功能，允許用戶在同一個 PDF 文件中選擇性地將某些內容設置為可見，將其他內容設置為不可見。PDF 圖層是分層藝術品、地圖和 CAD 圖紙中使用的常見元素。本文將演示如何使用Spire.PDF for .NET以編程方式在 PDF 文件中添加、隱藏或刪除圖層。

Spire.PDF for .NET 是一款獨立 PDF 控件，用于 .NET 程序中創建、編輯和操作 PDF 文檔。使用 Spire.PDF 類庫，開發人員可以新建一個 PDF 文檔或者對現有的 PDF 文檔進行處理，且無需安裝 Adobe Acrobat。

E-iceblue 功能類庫Spire 系列文檔處理組件均由中國本土團隊研發，不依賴第三方軟件，不受其他國家的技術或法律法規限制，同時適配國產操作系統如中科方德、中標麒麟等，兼容國產文檔處理軟件 WPS（如 .wps/.et/.dps 等格式

Spire.PDF for.net下載   Spire.PDF for java下載

安裝 Spire.PDF for .NET

首先，您需要將 Spire.PDF for.NET 包中包含的 DLL 文件作為引用添加到您的 .NET 項目中。 可以從此鏈接下載 DLL 文件，也可以通過安裝。

PM> Install-Package Spire.PDF

使用 C# 和 VB.NET 向 PDF 文檔添加圖層

Spire.PDF for .NET 提供了PdfDocument.Layers.AddLayer()方法在 PDF 文檔中添加圖層，然后您可以在 PDF 圖層上繪制文本、線條、圖像或形狀。詳細步驟如下。

• 創建一個PdfDocument實例。
• 使用PdfDocument.LoadFromFile()方法加載示例 PDF 文件。
• 使用PdfDocument.Layers.AddLayer(String)方法在 PDF 中添加指定名稱的圖層。或者，您也可以在添加圖層時使用PdfDocument.Layers.AddLayer(String, PdfVisibility)方法設置圖層的可見性。
• 使用PdfLayer.CreateGraphics()方法為該圖層創建畫布。
• 在畫布上繪制文本、圖像或其他元素。
• 使用PdfDocument.SaveToFile()方法保存結果文檔。

【C＃】

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

namespace AddLayersToPdf
{
class Program
{
static void Main(string[] args)
{
//Create a PdfDocument instance and load a sample PDF file
PdfDocument pdf = new PdfDocument();
pdf.LoadFromFile(@"C:\Users\Administrator\Desktop\Sample.pdf");

//Invoke AddLayerWatermark method to add a watermark layer
AddLayerWatermark(pdf);

//Invoke AddLayerHeader method to add a header layer
AddLayerHeader(pdf);

//Save to file
pdf.SaveToFile("AddLayers.pdf");
pdf.Close();
}

private static void AddLayerWatermark(PdfDocument doc)
{
//Create a layer named "Watermark"
PdfLayer layer = doc.Layers.AddLayer("Watermark");

//Create a font
PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 48), true);

//Specify the watermark text
string watermarkText = "CONFIDENTIAL";

//Get text size
SizeF fontSize = font.MeasureString(watermarkText);

//Calculate two offsets
float offset1 = (float)(fontSize.Width * System.Math.Sqrt(2) / 4);
float offset2 = (float)(fontSize.Height * System.Math.Sqrt(2) / 4);

//Get page count
int pageCount = doc.Pages.Count;

//Declare two variables
PdfPageBase page;
PdfCanvas canvas;

//Loop through the pages
for (int i = 0; (i < pageCount); i++)
{
page = doc.Pages[i];

//Create a canvas from layer
canvas = layer.CreateGraphics(page.Canvas);
canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2);
canvas.SetTransparency(0.4f);
canvas.RotateTransform(-45);

//Draw sting on the canvas of layer
canvas.DrawString(watermarkText, font, PdfBrushes.DarkBlue, 0, 0);
}
}
private static void AddLayerHeader(PdfDocument doc)
{
// Create a layer named "Header"
PdfLayer layer = doc.Layers.AddLayer("Header");

//Get page size
SizeF size = doc.Pages[0].Size;

//Specify the initial values of X and y
float x = 90;
float y = 40;

//Get page count
int pageCount = doc.Pages.Count;

//Declare two variables
PdfPageBase page;
PdfCanvas canvas;

//Loop through the pages
for (int i = 0; (i < pageCount); i++)
{
//Draw an image on the layer
PdfImage pdfImage = PdfImage.FromFile(@"C:\Users\Administrator\Desktop\img.jpg");
float width = pdfImage.Width;
float height = pdfImage.Height;
page = doc.Pages[i];
canvas = layer.CreateGraphics(page.Canvas);
canvas.DrawImage(pdfImage, x, y, width, height);

//Draw a line on the layer
PdfPen pen = new PdfPen(PdfBrushes.DarkGray, 2);
canvas.DrawLine(pen, x, (y + (height + 5)), (size.Width - x), (y + (height + 2)));
}
}
}
}

【VB.NET】

Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports Spire.Pdf.Graphics.Layer
Imports System.Drawing

Namespace AddLayersToPdf
Class Program
Private Shared Sub Main(ByVal args() As String)

'Create a PdfDocument instance and load a sample PDF file
Dim pdf As PdfDocument = New PdfDocument
pdf.LoadFromFile("C:\Users\Administrator\Desktop\Sample.pdf")

'Invoke AddLayerWatermark method to add a watermark layer
Program.AddLayerWatermark(pdf)

'Invoke AddLayerHeader method to add a header layer
Program.AddLayerHeader(pdf)

'Save to file
pdf.SaveToFile("AddLayers.pdf")
pdf.Close()
End Sub

Private Shared Sub AddLayerWatermark(ByVal doc As PdfDocument)

'Create a layer named "Watermark"
Dim layer As PdfLayer = doc.Layers.AddLayer("Watermark")

'Create a font
Dim font As PdfTrueTypeFont = New PdfTrueTypeFont(New Font("Arial", 48), True)

'Specify the watermark text
Dim watermarkText As String = "CONFIDENTIAL"

'Get text size
Dim fontSize As SizeF = font.MeasureString(watermarkText)

'Calculate two offsets
Dim offset1 As Single = CSng((fontSize.Width * System.Math.Sqrt(2) / 4))
Dim offset2 As Single = CSng((fontSize.Height * System.Math.Sqrt(2) / 4))

'Get page count
Dim pageCount As Integer = doc.Pages.Count

'Declare two variables
Dim page As PdfPageBase
Dim canvas As PdfCanvas

'Loop through the pages
Dim i As Integer = 0
While (i < pageCount)
page = doc.Pages(i)

'Create a canvas from layer
canvas = layer.CreateGraphics(page.Canvas)
canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2)
canvas.SetTransparency(0.4F)
canvas.RotateTransform(-45)

'Draw sting on the canvas of layer
canvas.DrawString(watermarkText, font, PdfBrushes.DarkBlue, 0, 0)
i = (i + 1)
i += 1
End While
End Sub

Private Shared Sub AddLayerHeader(ByVal doc As PdfDocument)

' Create a layer named "Header"
Dim layer As PdfLayer = doc.Layers.AddLayer("Header")

'Get page size
Dim size As SizeF = doc.Pages(0).Size

'Specify the initial values of X and y
Dim x As Single = 90
Dim y As Single = 40

'Get page count
Dim pageCount As Integer = doc.Pages.Count

'Declare two variables
Dim page As PdfPageBase
Dim canvas As PdfCanvas

'Loop through the pages
Dim i As Integer = 0
While (i < pageCount)

'Draw an image on the layer
Dim pdfImage As PdfImage = PdfImage.FromFile("C:\Users\Administrator\Desktop\img.jpg")
Dim width As Single = pdfImage.Width
Dim height As Single = pdfImage.Height
page = doc.Pages(i)
canvas = layer.CreateGraphics(page.Canvas)
canvas.DrawImage(pdfImage, x, y, width, height)

'Draw a line on the layer
Dim pen As PdfPen = New PdfPen(PdfBrushes.DarkGray, 2)
canvas.DrawLine(pen, x, (y + (height + 5)), (size.Width - x), (y + (height + 2)))
i += 1
End While
End Sub
End Class
End Namespace

在 C# 和 VB.NET 中設置 PDF 文檔中圖層的可見性

要設置現有圖層的可見性，您需要使用PdfDocument.Layers屬性通過其索引或名稱獲取指定的圖層，然后使用PdfLayer.Visibility屬性顯示或隱藏該圖層。詳細步驟如下。

• 創建一個PdfDocument實例。
• 使用PdfDocument.LoadFromFile()方法加載示例 PDF 文檔。
• 使用PdfDocument.Layers.Visibility屬性設置指定圖層的可見性。
• 使用PdfDocument.SaveToFile()方法保存結果文檔。

【C＃】

using Spire.Pdf;
using Spire.Pdf.Graphics.Layer;

namespace HideLayer
{
class Program
{
static void Main(string[] args)
{
//Create a PdfDocument instance
PdfDocument pdf = new PdfDocument();

//Load a sample PDF document
pdf.LoadFromFile("AddLayers.pdf");

//Hide a specified layer by index
pdf.Layers[0].Visibility = PdfVisibility.Off;

//Hide a specified layer by name
//pdf.Layers["Watermark"].Visibility = PdfVisibility.Off;

//Save the result document
pdf.SaveToFile("HideLayer.pdf");
}
}
}

【VB.NET】

Imports Spire.Pdf
Imports Spire.Pdf.Graphics.Layer

Namespace HideLayer
Class Program
Private Shared Sub Main(ByVal args() As String)

'Create a PdfDocument instance
Dim pdf As PdfDocument = New PdfDocument

'Load a sample PDF document
pdf.LoadFromFile("AddLayers.pdf")

'Hide a specified layer by index
pdf.Layers(0).Visibility = PdfVisibility.Off

'Hide a specified layer by name
'pdf.Layers["Watermark"].Visibility = PdfVisibility.Off;

'Save the result document
pdf.SaveToFile("HideLayer.pdf")
End Sub
End Class
End Namespace

使用 C# 和 VB.NET 刪除 PDF 文檔中的圖層

Spire.PDF for .NET 還允許您使用PdfDocument.Layers.RemoveLayer(String)方法按名稱刪除現有圖層。但請注意，PDF 圖層的名稱可能不是唯一的，此方法將刪除所有具有相同名稱的 PDF 圖層。詳細步驟如下。

• 創建一個PdfDocument實例。
• 使用PdfDocument.LoadFromFile()方法加載示例 PDF 文檔。
• 使用PdfDocument.Layers.RemoveLayer(String)方法根據名稱刪除指定圖層。
• 使用PdfDocument.SaveToFile()方法保存結果文檔。

【C＃】

using Spire.Pdf;

namespace DeleteLayer
{
class Program
{
static void Main(string[] args)
{
//Create a PdfDocument instance
PdfDocument pdf = new PdfDocument();

//Load a sample PDF document
pdf.LoadFromFile("AddLayers.pdf");

//Remove a layer by name
pdf.Layers.RemoveLayer(("Watermark"));

//Save the result document
pdf.SaveToFile("DeleteLayer.pdf", FileFormat.PDF);
}
}
}

【VB.NET】

Imports Spire.Pdf

Namespace DeleteLayer
Class Program
Private Shared Sub Main(ByVal args() As String)
'Create a PdfDocument instance
Dim pdf As PdfDocument = New PdfDocument

'Load a sample PDF document
pdf.LoadFromFile("AddLayers.pdf")

'Remove a layer by name
pdf.Layers.RemoveLayer("Watermark")

'Save the result document
pdf.SaveToFile("DeleteLayer.pdf", FileFormat.PDF)
End Sub
End Class
End Namespace

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