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. https://docs.fileformat.com/pdf/ua/

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