14.3.1 PDF/A: PDF for Archiving
The PDF/A format is a subset of the regular PDF format with certain features, deemed incompatible
with long-term archival and storage of documents, removed. PDF/A-compliant
documents must be completely self-contained, with no reliance on external resources.
The single most important requirement for PDF/A files is that all fonts must be embedded.
Other requirements include:
- Encryption is not allowed;
- Documents must contain standards-based metadata;
- Links to other documents and URLs are not allowed.
- Use of device-dependent color spaces such as DeviceRGB is only allowed with some restrictions.
- Certain other PDF features, such as JavaScript, XML Forms Architecture (XFA), LZW compression, and others, are not allowed.
There are currently three levels of PDF/A conformance: PDF/A-1, PDF/A-2 and PDF/A-3, with Level 1 subdivided into sublevels A and B.
For more information on PDF/A, see http://www.pdfa.org.
14.3.2 AspPDF.NET's Support for PDF/A
UPDATE: As of Version 3.7, PDF/A-3 is supported as well. See
Section 14.3.4 for details.
As of Version 3.3, AspPDF.NET is capable of producing PDF documents compliant with PDF/A-1b,
the basic conformance level which ensures reliable reproduction of the visual appearance of the document.
Even prior to Version 3.3, AspPDF.NET embedded all TrueType fonts and allowed metadata to be specified, thus meeting the most important PDF/A requirements.
Version 3.3 bridges the remaining gap to full PDF/A-1b compliance by implementing the following features and enhancements:
- The new PdfDocument.AddOutputIntent method enables mapping from a device-dependent color space such as DeviceRGB
to a device-independent color space via an International Color Consortium (ICC) profile, thus satisfying the
media-independent visual color reproduction requirement.
- The entries /CIDToGIDMap and /CIDSet have been implemented for embedded TrueType fonts.
- A bug has been fixed responsible for certain stream objects to lack the required end-of-line character before the keyword endstream.
The AddOutputIntent method expects 4 arguments: the output condition, the output condition indentifier, the path to the .icc profile file,
and the number of color components in the device-dependent color space used by the document (1 for DeviceGray, 3 for DeviceRGB and 4 for DeviceCMYK.)
The output condition is a string concisely identifying the intended output device or production condition in human-readable form. The output condition identifier
is a string that identifies the output device or production condition as it appears in an industry-standard registry, and can be set to "Custom".
The metadata format is XML-based and similar to that described in the previous section of this chapter, but
must contain additional tags. The following example is a minimal metadata string required for PDF/A-1b compliance:
<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta x:xmptk="Adobe XMP Core 4.2.1-c041 52.342996, 2008/05/07-20:48:00" xmlns:x="adobe:ns:meta/">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="" xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/">
<pdfaid:part>1</pdfaid:part>
<pdfaid:conformance>B</pdfaid:conformance>
</rdf:Description>
<rdf:Description rdf:about="" xmlns:pdf="http://ns.adobe.com/pdf/1.3/">
<pdf:Producer>Persits Software AspPDF.NET - www.persits.com</pdf:Producer>
<pdf:Keywords></pdf:Keywords>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>
There are several components of this metadata string that are worth noting:
- The metadata must be enclosed within the <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
and <?xpacket end="w"?> tags.
- The PDF/A level of conformance must be specified via the <pdfaid:part>
and <pdfaid:conformance> tags (1 and B for AspPDF.NET's level of conformance.)
- The Producer value must match the current value for the PdfDocument.Producer property which is set to "Persits Software AspPDF for .NET - www.persits.com" by default.
In addition to the tags shown above, PDF/A metadata almost always contains "Dublin Core" (DC) tags as well,
such as <dc:title> and <dc:description>, for example:
<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta x:xmptk="Adobe XMP Core 4.2.1-c041 52.342996, 2008/05/07-20:48:00" xmlns:x="adobe:ns:meta/">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
...
<rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
<dc:title>
<rdf:Alt>
<rdf:li xml:lang="x-default">Sunset on the beach</rdf:li>
<rdf:li xml:lang="de-DE">Sonnenuntergang am Strand</rdf:li>
</rdf:Alt>
</dc:title>
<dc:description>
<rdf:Alt>
<rdf:li xml:lang="x-default">Hello, World</rdf:li>
<rdf:li xml:lang="de-DE">Hallo, Welt</rdf:li>
</rdf:Alt>
</dc:description>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>
14.3.3 Code Sample
The following code sample creates a PDF/A-1b compliant document by importing the URL http://www.asppdf.net,
attaching the metadata from the text file metadata.txt located in the same folder as the code sample,
and adding an output intent based on the color profile AdobeRGB1998.icc located in the sibling folder manual_16
of the installation.
The content of the file metadata.txt is as follows:
<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta x:xmptk="Adobe XMP Core 4.2.1-c041 52.342996, 2008/05/07-20:48:00" xmlns:x="adobe:ns:meta/">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="" xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/">
<pdfaid:part>1</pdfaid:part>
<pdfaid:conformance>B</pdfaid:conformance>
</rdf:Description>
<rdf:Description rdf:about="" xmlns:pdf="http://ns.adobe.com/pdf/1.3/">
<pdf:Producer>Persits Software AspPDF for .NET - www.persits.com</pdf:Producer>
<pdf:Keywords></pdf:Keywords>
</rdf:Description>
<rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
<dc:title>
<rdf:Alt>
<rdf:li xml:lang="x-default">@@@title@@@</rdf:li>
</rdf:Alt>
</dc:title>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>
Note that this metadata file is actually a template, it contains the placeholder @@@title@@@
where the actual title should be. The code sample replaces the placeholder with the value of the PdfDocument.Title
property (which is not known in advance since ImportFromUrl sets it based on the HTML content it imports)
to ensure that the document's Title entry and the value of the <dc:title>
tag in the metadata match.
| C# |
|---|
PdfManager objPdf = new PdfManager();
// Create empty document
PdfDocument objDoc = objPdf.CreateDocument();
// Convert HTML to PDF
objDoc.ImportFromUrl("http://www.asppdf.net", "landscape=true; scale=0.75");
// Add metadata from a file
string strMetadata = objPdf.LoadTextFromFile(Server.MapPath("metadata.txt"));
// Replace placeholder with actual document title
strMetadata = strMetadata.Replace("@@@title@@@", objDoc.Title);
objDoc.MetaData = strMetadata;
// Add output intent using an RGB color profile. Borrow .icc file from Chapter 15
string strProfilePath = Server.MapPath(".") + @"\..\manual_16\AdobeRGB1998.icc";
objDoc.AddOutputIntent("AdobeRGB", "Custom", strProfilePath, 3);
// Save document
string strPath = Server.MapPath("pdfa.pdf");
string strFileName = objDoc.Save(strPath, false);
|
| VB.NET |
|---|
Dim objPdf As PdfManager = New PdfManager()
' Create empty document
Dim objDoc As PdfDocument = objPdf.CreateDocument()
' Convert HTML to PDF
objDoc.ImportFromUrl("http://www.asppdf.net", "landscape=true; scale=0.75")
' Add metadata from a file
Dim strMetadata As String = objPdf.LoadTextFromFile(Server.MapPath("metadata.txt"))
' Replace placeholder with actual document title
strMetadata = strMetadata.Replace("@@@title@@@", objDoc.Title)
objDoc.MetaData = strMetadata
' Add output intent using an RGB color profile. Borrow .icc file from Chapter 15
Dim strProfilePath As String = Server.MapPath(".") + "\..\manual_16\AdobeRGB1998.icc"
objDoc.AddOutputIntent("AdobeRGB", "Custom", strProfilePath, 3)
' Save document
Dim strPath As String = Server.MapPath("pdfa.pdf")
Dim strFileName As String = objDoc.Save(strPath, false)
|
Click the links below to run this code sample:
http://localhost/asppdf.net/manual_14/14_pdfa.cs.aspx
http://localhost/asppdf.net/manual_14/14_pdfa.vb.aspx
14.3.4 PDF/A-3 Compliance
As of Version 3.7, AspPDF.NET is capable of producing PDF documents with the highest, PDF/A-3, level of compliance. The changes involved
small additions to, and modifications in, various internal PDF objects, as well as a major new feature.
14.3.4.1 The List of Changes
The following small changes have been made to AspPDF.NET's PDF-generating engine to make PDF/A-3 validators happy:
- The document catalog now has the attribute MarkInfo and it is set to true.
- The value of the CIDSet attribute of the font object, supported since version 3.3, is now computed differently to be compatible with PDF/A-3 specifications.
- The font's ToUnicode character map has been modified to fit PDF/A-3 requirements.
- Link annotations internally created by ImportFromUrl and DrawText methods to display clickable URLs are now marked printable by default,
which is apparently a PDF/A-3 requirement. In previous versions, link annotations had the print flag cleared by default.
- FileAttachment annotations now has the Subtype attribute set to the embedded file's MIME type such as "text/html". PDF/A-3 apparently requires this attribute.
- The ICC profile added by the AddOutputIntent method now has the Info attribute, which AspPDF.NET sets arbitrarily to the profile's filename.
This attribute is apparently yet another PDF/A-3 requirement.
- When creating a FileAttachment annotations, two new parameters, Names=true, and AF=<value between 0 and 6> need to be passed to the PdfAnnots.Add method.
The Names parameter, when set to True, instructs AspPDF.NET to put the new annotation object in the document catalog's Names array instead of the Annots array,
where it would normally reside.
The AF parameter, which stands for "associated files relationship", is responsible for adding the AFRelationship entry to the file annotation object, which is yet another PDF/A-3 requirement,
The AF value can be one of the following: 0 (Source), 1 (Data), 2 (Alternative), 3 (Supplement), 4 (Unspecified), 5 (EncryptedPayload) and 6 (None).
- All FileAttachment annotations must be included in the logical structure tree by calling the method AddStructureElement introduced in Version 3.7.
The tree's root is represented by the entry StructTreeRoot which is added to the document catalog.
Even if there are no FileAttachment annotations, the document still must contain a logical structure tree (possibly with no nodes) to be PDF/A-3 compliant.
AddStructureElement is described in detail below.
14.3.4.2 Logical Structure Tree
PDF's logical structure facilities provide a mechanism for incorporating structural information about a document's content into a PDF file.
Such information might include, for example, the organization of the document into chapters and sections or the identification of special elements such as figures, tables,
and footnotes.
As of Version 3.7, AspPDF.NET provides limited support for the logical structure trees via the methods BeginMarkedContent, EndMarkedContent, and
AddStructureElement.
When a drawing operation such as a call to PdfCanvas.DrawText, or a group of such operations, is sandwitched between a call to PdfCanvas.BeginMarkedContent and PdfCanvas.EndMarkedContent,
the content drawn by these operations become marked content with a unique ID. The ID is returned by the BeginMarkedContent method. This marked content ID can then be put in the
logical structure tree via a subsequent call to AddStructureElement.
The PdfDocument.AddStructureElement method places a structure element onto the logical structure tree and returns a unique item ID of the newly placed item,
The method expects 5 arguments:
- Item: an image, graphics or annotation object, or a marked content ID returned by BeginMarkedContent. Can also be set to Nothing (null) for an empty structure element.
- Type: a string describing the item. Although arbitrary names are generally allowed, PDF/A-3 compliance requires that a standard type should be used.
The standard types include: Document, Part, Art, Sect, Div, Caption, TOC (table of content), TOCI (table of contents item),
Index, NonStruct, Private,
H, H1-H6 (headers), P (paragraph), L (list), LI (list item), Lbl (label), LBody (list body), Table, TR (table row),
TH (table header), TD (table data cell),
THead (table header row group), TBody (table body row group), TFoot (table footer row group), Span, Quote, Note, Reference, BibEntry (bibliography reference),
Code, Link, Annot, Rudy, Warichu, and others.
- ParentID: the ID of a structure element added by a previous call to the AddStructureElement method. Must be set to 0 for the root element.
- Page: an instance of the PdfPage object associated with this structure element. Can be set to Nothing (null).
- Params: reserved for future use. Must be set to an empty string.
For PDF/A-3 compliance, the PDF document must at least have an empty root structure element. The following code sample generates a PDF/A-3 compliant document.
It is almost identical to the previous code sample, but adds an empty root element and replaces the "1B" designation (PDF/A-1B) with "3A" (PDF/A-3) in the metadata:
| C# |
|---|
...
// PDF/A-3 specific: specify A3 instead of B1 in metadata, add empty structure element
strMetadata = strMetadata.Replace("<pdfaid:part>1</pdfaid:part>", "<pdfaid:part>3</pdfaid:part>");
strMetadata = strMetadata.Replace("<pdfaid:conformance>B</pdfaid:conformance>", "<pdfaid:conformance>A</pdfaid:conformance>");
objDoc.AddStructureElement(null, "Document", 0, null, "");
...
|
| VB.NET |
|---|
...
' PDF/A-3 specific: specify A3 instead of B1 in metadata, add empty structure element
strMetadata = strMetadata.Replace("<pdfaid:part>1</pdfaid:part>", "<pdfaid:part>3</pdfaid:part>")
strMetadata = strMetadata.Replace("<pdfaid:conformance>B</pdfaid:conformance>", "<pdfaid:conformance>A</pdfaid:conformance>")
objDoc.AddStructureElement(Nothing, "Document", 0, Nothing, "")
...
|
Click the links below to run this code sample:
http://localhost/asppdf.net/manual_14/14_pdfa3.cs.aspx
http://localhost/asppdf.net/manual_14/14_pdfa3.vb.aspx
The following code snippet demonstrates the creation of a meaningful logical structure tree with the document element at the root,
a section element, and title and two paragraph elements within this chapter element. Also it adds a FileAttachment annotation to
the document and adds a structure element for this annotation, which is required for PDF/A-3 compliance:
| C# |
|---|
PdfManager objPdf = new PdfManager();
PdfDocument objDoc = objPdf.CreateDocument();
int DocID = objDoc.AddStructureElement(null, "Document", 0, null, "");
int SectID = objDoc.AddStructureElement(null, "Sect", DocID, null, "");
PdfPage objPage = objDoc.Pages.Add();
int HeaderID = objPage.Canvas.BeginMarkedContent();
objPage.Canvas.DrawText( "Header", "x=10; y=700", objDoc.Fonts["Arial"] );
objPage.Canvas.EndMarkedContent();
int P1ID = objPage.Canvas.BeginMarkedContent();
objPage.Canvas.DrawText( "Paragraph 1", "x=10; y=500", objDoc.Fonts["Arial"] );
objPage.Canvas.EndMarkedContent();
int P2ID = objPage.Canvas.BeginMarkedContent();
objPage.Canvas.DrawText( "Paragraph 2", "x=10; y=300", objDoc.Fonts["Arial"] );
objPage.Canvas.EndMarkedContent();
objDoc.AddStructureElement( HeaderID, "H", SectID, objPage, "" );
objDoc.AddStructureElement( P1ID, "P", SectID, objPage, "" );
objDoc.AddStructureElement( P2ID, "P", SectID, objPage, "" );
PdfAnnot objAnnot = objPage.Annots.Add("", "x=1,y=700;width=10;height=10; Type=FileAttachment; names=true; AF=0;", "Paperclip", @"C:\path\factur-x.xml");
objDoc.AddStructureElement( objAnnot, "Annot", DocID, objPage, "" );
...
|
| VB.NET |
|---|
Dim objPdf As PdfManager = New PdfManager()
Dim objDoc As PdfDocument = objPdf.CreateDocument()
Dim DocID As Integer = objDoc.AddStructureElement(Nothing, "Document", 0, Nothing, "")
Dim SectID As Integer = objDoc.AddStructureElement(Nothing, "Sect", DocID, Nothing, "")
Dim objPage As PdfPage = objDoc.Pages.Add()
Dim HeaderID As Integer = objPage.Canvas.BeginMarkedContent()
objPage.Canvas.DrawText( "Header", "x=10; y=700", objDoc.Fonts("Arial") )
objPage.Canvas.EndMarkedContent()
Dim P1ID As Integer = objPage.Canvas.BeginMarkedContent()
objPage.Canvas.DrawText( "Paragraph 1", "x=10; y=500", objDoc.Fonts("Arial") )
objPage.Canvas.EndMarkedContent()
Dim P2ID As Integer = objPage.Canvas.BeginMarkedContent()
objPage.Canvas.DrawText( "Paragraph 2", "x=10; y=300", objDoc.Fonts("Arial") )
objPage.Canvas.EndMarkedContent()
objDoc.AddStructureElement( HeaderID, "H", SectID, objPage, "" )
objDoc.AddStructureElement( P1ID, "P", SectID, objPage, "" )
objDoc.AddStructureElement( P2ID, "P", SectID, objPage, "" )
Dim objAnnot As PdfAnnot = objPage.Annots.Add("", "x=1,y=700;width=10;height=10; Type=FileAttachment; names=true; AF=0;", "Paperclip", "C:\path\factur-x.xml")
objDoc.AddStructureElement( objAnnot, "Annot", DocID, objPage, "" )
|
