Pdf-lib: [Feature Request]: Generate PDF/A-3 documents

[zimt28]

This is the second half of my feature requests, see: https://github.com/Hopding/pdf-lib/issues/229.

It would be great if pdf-lib could generate PDF/A-3 documents, which in my case are required by the ZUGFeRD specification.

[Hopding]

Hello @zimt28! This is an interesting idea. What exactly do you envision this feature looking like?

As far as I can tell, the PDF/A standard is just a subset of the PDF standard. Since pdf-lib adheres to the PDF 1.7 spec, I would think that all you need to do to generate a PDF/A document with pdf-lib is simply not use the PDF features that are disallowed in PDF/A. Or put another way, generating a PDF/A document with pdf-lib shouldn't require any new features. It just means not using particular tools offered by pdf-lib.

[13thirteen]

Hi! First of all thank you so much @Hopding for this awesome library!

I'm not the original poster of this issue, but I'm also interested in generating PDF/A documents. So, I tried to generate a valid PDF/A-3B document with the help of veraPDF (a PDF/A conformance checker).
Apparently, it's not enough to leave away certain PDF features. Some things need to be added.

Here are my findings:

• Rule: The catalog dictionary shall contain the Metadata key with a metadata stream as value
  
  
  
  • I added XMP metadata again (in addition to the metadata setters introduced in release 1.2.0) as explained in https://github.com/Hopding/pdf-lib/issues/55#issuecomment-527447921
  
  
  • This gave me a followup error violating this rule
  
  
  • I had to remove the line <pdf:Subject>${options.subject}</pdf:Subject> to fix this.
  
  
• Rule: The PDF/A version and conformance level shall be specified in XMP metadata
  
  
  
  • For this, I added the following lines just before the closing </rdf:RDF> in the XMP metadata added above:
    
    <rdf:Description rdf:about="" xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/"> <pdfaid:part>3</pdfaid:part> <pdfaid:conformance>B</pdfaid:conformance> </rdf:Description>
  
  
• Rule: The file trailer dictionary shall contain the ID keyword
  
  
  
  • I used the following code to add file identifiers (see also PDF 1.7 specification chapter 14.4)
    
    const encoder = new TextEncoder(); const data = ... // Use document information and current time to make the identifier unique const hash = await crypto.subtle.digest('SHA-512', data); const hashArray = Array.from(new Uint8Array(hash)); const hashHex = hashArray.map((b) => b.toString(16).padStart(2, '0')).join(''); const permanent = PDFHexString.of(hashHex); const changing = permanent; doc.context.trailerInfo.ID = doc.context.obj([permanent, changing]);
  
  
• Rule: DeviceRGB shall only be used (...) if the file has a PDF/A OutputIntent that contains an RGB destination profile
  
  
  
  • I was able to add the ICC v2 sRGB color profile (file sRGB2014.icc from http://www.color.org/srgbprofiles.xalter#v2) as follows:
    
    ```
    
    public static setColorProfile(doc: PDFDocument) {
    
    const profile = ...; // Content of file sRGB2014.icc
    
    const profileStream = doc.context.stream(profile, {
    
    Length: profile.length,
    
    });
    
    const profileStreamRef = doc.context.register(profileStream);
  
  

    const outputIntent = doc.context.obj({
      Type: 'OutputIntent',
      S: 'GTS_PDFA1',
      OutputConditionIdentifier: PDFString.of('sRGB'),
      DestOutputProfile: profileStreamRef,
    });
    const outputIntentRef = doc.context.register(outputIntent);
    doc.catalog.set(PDFName.of('OutputIntents'), doc.context.obj([outputIntentRef]));
  }
```

• In my document, I added a link annotation as explained in https://github.com/Hopding/pdf-lib/issues/161#issuecomment-523186749
  
  
  
  • This gave me validation errors for this rule and that rule
  
  
  • I had to add F: 4, (setting the Print flag) to the annotation dictionary.
  
  
• In my document, I am embedding a custom TrueType font (Liberation Sans) which leads to the following validation error:
  
  
  
  • Rule: All embedded Type 2 CIDFonts in the CIDFont dictionary shall contain a CIDToGIDMap entry that shall be a stream mapping from CIDs to glyph indices or the name Identity
  
  
  • This is the only validation error that I was not able to resolve by myself (yet).
  
  
  • Maybe such a CIDToGIDMap could be added in CustomFontEmbedder.ts somehow?
  
  

(Disclaimer: I'm not sure if my code snippets are clean & correct. At least, they removed (almost all) the veraPDF validation errors for my specific use case. There might be further issues for other PDF features. @Hopding feel free to edit the code snippets if you see need.)

Edit: Oh, and Happy New Year!

[dotob]

this would be great as there are not other pure js libs doing this.

[DkDavid]

Just came accross this issue because I am working on adding factur-x conformance, which needs PDF-A3 conformance.
@13thirteen Your information was very helpful. Regarding your last point:
I added the following to the file "CustomFontEmbedder.ts" and achieved full PDFA-3 compliance:
In the function embedCIDFontDict I changed
const cidFontDict = context.obj({
Type: 'Font',
Subtype: this.isCFF() ? 'CIDFontType0' : 'CIDFontType2',
BaseFont: this.baseFontName,
...
to:

const cidFontDict = context.obj({
Type: 'Font',
Subtype: this.isCFF() ? 'CIDFontType0' : 'CIDFontType2',
CIDToGIDMap: 'Identity',
BaseFont: this.baseFontName,
...

[maximebochon]

Similarly, I would like to be able to choose the specification version (1.4, ..., 1.7) of the PDF document produced by pdf-lib. This would make it possible to start from an 1.7 document and remove from it features that are too recent in order to keep only the compatible part.