1.什么是PDF/UA文件

PDF/UA，即Universally Accessible PDF，该格式的PDF文件是于2012年8月以ISO标准14289-1发布的、具有普遍可访问的PDF文档标准。为带标签的PDF文档（Tagged PDF Document）和表单的开发人员和作者设定了明确的规则。（PDF/UA-1是作为PDF/UA标准的第一部分，PDF/UA-2作为PDF/UA标准的第二部分）[1]

2.文件格式要求

PDF/UA在其基础上有着明确的要求，即该标准都是基于PDF标签，所有PDF/UA文档都必须以PDF标签来正确标记，并且，要求标签在语义上适当，并按逻辑顺序排列。[1]

3.如何创建PDF/UA文件

PDF/UA文件作为PDF文件的一种标准格式，要创建该标准的的PDF文档，可使用调用PDF API的方法来创建。下面，是以Spire.PDF for .NET来创建的方法。

注：可在Visual Studio 中通过NuGet搜索“Spire.PDF”安装dll到程序中；

或者下载包（hotfix版本）到本地，手动添加本地路径下的Spire.Pdf.dll文件到程序。

C#

using Spire.Pdf;
using Spire.Pdf.Graphics;
using Spire.Pdf.Interchange.TaggedPdf;
using System.Drawing;
namespace CreatePDFUAfile
{
 class Program
    {
 static void Main(string[] args)
        {
            //创建PdfDocument类的对象
            PdfDocument doc = new PdfDocument();
 
             //添加一页
            doc.Pages.Add();
 
             //设置tab order
            doc.Pages[0].SetTabOrder(TabOrder.Structure);
 
             //创建PdfTaggedContent类的对象
            PdfTaggedContent taggedContent = new PdfTaggedContent(doc);
            taggedContent.SetLanguage("en-US");
            taggedContent.SetTitle("test");
 
             //设置PDF/UA1验证
            taggedContent.SetPdfUA1Identification();
 
             //创建字体、画刷
            PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Times New Roman", 10), true);
            PdfSolidBrush brush = new PdfSolidBrush(Color.Black);
 
             //添加要素
            PdfStructureElement article = taggedContent.StructureTreeRoot.AppendChildElement(PdfStandardStructTypes.Document);
            PdfStructureElement paragraph1 = article.AppendChildElement(PdfStandardStructTypes.Paragraph);
            PdfStructureElement span1 = paragraph1.AppendChildElement(PdfStandardStructTypes.Span);
            span1.BeginMarkedContent(doc.Pages[0]);
            PdfStringFormat format = new PdfStringFormat(PdfTextAlignment.Justify);
            doc.Pages[0].Canvas.DrawString("PDF/UA was published as ISO Standard 14289-1 in August 2012" +
 " and is by far the first complete definition " +
 "of a set of requirements for universally accessible PDF documents.",
               font, brush, new Rectangle(40, 80, 450, 80), format);
            span1.EndMarkedContent(doc.Pages[0]);
            PdfStructureElement paragraph2 = article.AppendChildElement(PdfStandardStructTypes.Paragraph);
            paragraph2.BeginMarkedContent(doc.Pages[0]);
            doc.Pages[0].Canvas.DrawString("The PDF/UA has some definite requirements at its base that act as the essence of this standard.",
               font, brush, new Rectangle(40, 120, 450, 60), format);
            paragraph2.EndMarkedContent(doc.Pages[0]);
            PdfStructureElement figure1 = article.AppendChildElement(PdfStandardStructTypes.Figure);
             //Set Alternate text 
            figure1.Alt = "replacement text1";
            figure1.BeginMarkedContent(doc.Pages[0], null);
            PdfImage image = PdfImage.FromFile(@"logo.jpg");
            doc.Pages[0].Canvas.DrawImage(image, new PointF(40, 200), new SizeF(100, 100));
            figure1.EndMarkedContent(doc.Pages[0]);
            PdfStructureElement figure2 = article.AppendChildElement(PdfStandardStructTypes.Figure);
             //Set Alternate text
            figure2.Alt = "replacement text2";
            figure2.BeginMarkedContent(doc.Pages[0], null);
            doc.Pages[0].Canvas.DrawRectangle(PdfPens.Black, new Rectangle(300, 200, 100, 100));
            figure2.EndMarkedContent(doc.Pages[0]);
             //保存文档
            doc.SaveToFile("CreatePDFUAFile_result.pdf");
            System.Diagnostics.Process.Start("CreatePDFUAFile_result.pdf");
        }
    }
}

VB.NET

Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports Spire.Pdf.Interchange.TaggedPdf
Imports System.Drawing
 
Namespace CreatePDFUAfile
	Class Program
		Private Shared Sub Main(args As String())
			'创建PdfDocument类的对象
			Dim doc As New PdfDocument()
 
			'添加一页
			doc.Pages.Add()
 
			'设置tab order
			doc.Pages(0).SetTabOrder(TabOrder.[Structure])
 
			'创建PdfTaggedContent类的对象
			Dim taggedContent As New PdfTaggedContent(doc)
			taggedContent.SetLanguage("en-US")
			taggedContent.SetTitle("test")
 
			'设置PDF/UA1验证
			taggedContent.SetPdfUA1Identification()
 
			'创建字体、画刷
			Dim font As New PdfTrueTypeFont(New Font("Times New Roman", 10), True)
			Dim brush As New PdfSolidBrush(Color.Black)
 
			'添加要素
			Dim article As PdfStructureElement = taggedContent.StructureTreeRoot.AppendChildElement(PdfStandardStructTypes.Document)
			Dim paragraph1 As PdfStructureElement = article.AppendChildElement(PdfStandardStructTypes.Paragraph)
			Dim span1 As PdfStructureElement = paragraph1.AppendChildElement(PdfStandardStructTypes.Span)
			span1.BeginMarkedContent(doc.Pages(0))
 
			Dim format As New PdfStringFormat(PdfTextAlignment.Justify)
			doc.Pages(0).Canvas.DrawString("PDF/UA was published as ISO Standard 14289-1 in August 2012" + " and is by far the first complete definition " + "of a set of requirements for universally accessible PDF documents.", font, brush, New Rectangle(40, 80, 450, 80), format)
			span1.EndMarkedContent(doc.Pages(0))
 
			Dim paragraph2 As PdfStructureElement = article.AppendChildElement(PdfStandardStructTypes.Paragraph)
			paragraph2.BeginMarkedContent(doc.Pages(0))
			doc.Pages(0).Canvas.DrawString("The PDF/UA has some definite requirements at its base that act as the essence of this standard.", font, brush, New Rectangle(40, 120, 450, 60), format)
			paragraph2.EndMarkedContent(doc.Pages(0))
 
			Dim figure1 As PdfStructureElement = article.AppendChildElement(PdfStandardStructTypes.Figure)
			'Set Alternate text 
			figure1.Alt = "replacement text1"
			figure1.BeginMarkedContent(doc.Pages(0), Nothing)
			Dim image As PdfImage = PdfImage.FromFile("logo.jpg")
			doc.Pages(0).Canvas.DrawImage(image, New PointF(40, 200), New SizeF(100, 100))
			figure1.EndMarkedContent(doc.Pages(0))
 
			Dim figure2 As PdfStructureElement = article.AppendChildElement(PdfStandardStructTypes.Figure)
			'Set Alternate text
			figure2.Alt = "replacement text2"
			figure2.BeginMarkedContent(doc.Pages(0), Nothing)
			doc.Pages(0).Canvas.DrawRectangle(PdfPens.Black, New Rectangle(300, 200, 100, 100))
			figure2.EndMarkedContent(doc.Pages(0))
 
			'保存文档
			doc.SaveToFile("CreatePDFUAFile_result.pdf")
			System.Diagnostics.Process.Start("CreatePDFUAFile_result.pdf")
		End Sub
	End Class
End Namespace

参考资料：

1. PDF/UA File Format

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