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