Skip to main content

Generating PDF/A From HTML in Meteor


My live-chat app was a folk of project Rocket.Chat which was built with Meteor. The app had a feature that administrative users were able to export the conversations into PDF files. And, they wanted to archive these files for a long time.

I happened to know that PDF/A documents were good for this purpose. It was really frustrated to find a solution with free libraries. Actually, it took me more than two weeks to find a possible approach.

TL, DR;
Using Puppeteer to generate a normal PDF and using PDFBox to load and converting the generated PDF into PDF/A compliance.

What is PDF/A?

Here is a definition from Wikipedia:
PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for use in the archiving and long-term preservation of electronic documents. PDF/A differs from PDF by prohibiting features unsuitable for long-term archiving, such as font linking (as opposed to font embedding) and encryption. The ISO requirements for PDF/A file viewers include color management guidelines, support for embedded fonts, and a user interface for reading embedded annotations.

Why PDF/A documents matter

In my point of view, it’s a standard file for archiving thanks to key features:
  • The fonts of document’s content will always be displayed the same on all places, not depending on any devices.
  • Documents are safe. For example, no executable file launches are allowed or no external content references are allowed.
(Find more features at https://en.wikipedia.org/wiki/PDF/A#Description)

Several approaches for creating a PDF/A document

At the first glance, I found some approaches as follows:

(1). Paid APIs
  • Aspose PDF: Java-based APIs. It seemed the price was too expensive.
  • PdfTron: Javascript-based APIs. I tried to contact them to know the price but they requested me some information even I could not estimate to answer it.
(2). Free APIs
  • Apache FOP: Java-based APIs. I needed to defined the templates by its own ways (FOP files) instead of HTML and CSS. (I created a hello world app here)
  • PDFBox: Java-based APIs. It looked promising that I could convert a normal PDF document to PDF/A one.
(3). Forking a open source project/building my own PDF/A generating engine
  • pdfkit: Javascript-based project. I needed to know the specification of PDF/A compliance, and to build my own lib for generating PDF/A documents.
Basing on these insights, I decided to go with approach (2).

Apache FOP tryout

I decided to stop this approach. Apache FOP strictly required to provide templates with XSL-FO format which is not supported wisely. Ref: https://stackoverflow.com/questions/10641667/use-of-xsl-fo-css3-instead-of-css2-to-create-paginated-documents-like-pdf/21345708#21345708
  • Due to limitation of formatting support, it’s hard to format content of a PDF if its template is complex such as including images, tables, etc..
  • There seemed to be no tools for converting from HTML, CSS into XSL-FO. But my templates were built on HTML, CSS and Meteor and data was bound dynamically.

PDFBox tryout

Basing on the example of creating PDF/A here, I tried to convert an existing normal PDF file into another PDF/A. There were 3 parts to do:
  1. embed/load fonts
  2. include XMP metadata
  3. include color profile
I used these following tools to verify the result:
With filling some mandatory information, I passed the parts 2 and 3 successfully. But, I have really got stuck at part 1 for a long time.

Eventually, I found the root cause by delving deeper into source code of some libraries PDFBox, PDFBox Preflight, node-html-pdf, PhantomJS, etc.. as follows:

I could not successfully generate PDF/A document by converting the existing normal PDFs generated from Meteor because the PDF generated did not embedded the font fully.

My project used node-html-pdf which in turn used PhantomJS to render HTML into PDF. PhantomJS used Qt for writing PDF. The library always embedded the fonts using Subsetting (meaning only the characters were used in the document were embedded). This did not comply with the PDF/A specification.

I couldn’t do anything here because PhantomJS used a very old version of Qt (only Qt v5.x onwards supported PDA/A). The PhantomJS was also discontinued since Mar 2018.

Besides, I could not use PDFBox to embed fonts fully either. There was a method PDType0Font.load for loading fonts but it also embedded the fonts using Subsetting.

Yay! It worked

I discovered that by replacing the process rendering HTML to PDF with the fonts fully embedded.
Using a different library to replace PhantomJS, I found Google Chrome’s Puppeteer.

Then, I could use PDFBox to convert the normal PDF to PDF/A with including XMP metadata and color profile.


References:
[1]. https://www.youtube.com/watch?v=EqII7ilmY8o&feature=youtu.be
[2]. https://stackoverflow.com/questions/38737219/how-to-convert-pdf-to-pdf-a-in-java
[3].http://svn.apache.org/repos/asf/pdfbox/trunk/preflight/src/main/java/org/apache/pdfbox/preflight/PreflightConstants.java
[4]. http://www.pdf-tools.com/public/downloads/whitepapers/whitepaper-pdfa.pdf
[5]. https://medium.com/@raphaelstbler/advanced-pdf-generation-for-node-js-using-puppeteer-e168253e159c
Labels:

Comments

Post a Comment

Popular posts from this blog

Tip for resolving the compile errors when importing a Maven project in Eclipse

Sometimes, I import a existing Maven project into Eclipse and I get some compile errors related to "pom.xml", "facet version of Web", and  so on. It was really frustrating me because I even cleaned, built and updated the project many times but the errors still occurred. I accidentally found the following steps to resolve this issue but honestly I still don't know why. Step 1 : Delete the project that met the compile errors in Eclipse, but don't delete it on disk. Step 2 : Open the project (by Windows Explorer if you use Windows) and remove  file/folder ".classpath", ".settings" and ".project" . Step 3 : Import the project back into Eclipse. ---^0^--- Maven is a build automation tool used primarily for Java projects. Eclipse is an integrated development environment (IDE).
Post a Comment
Read more

Monday vhandit #1

This is the first post in a series of articles called "Monday vhandit". You can go to the original post by clicking on each head title. Character encodings: essential concepts This article points out why Unicode matters and differentiates among concepts: character sets, coded character set (unit is code points), and character encoding. Explained from First Principles: the Internet The very structural and well-explained article contains almost concepts of the Internet. I really appreciated the author's effort put on that post. Dev Community - DevDojo I just joined this community. DevDojo is really a developer-oriented platform. It is very nice, easy, fast, and sufficient to write (Markdown supported) and search for a post. The best of it, you also have a personal blog for your posts at "<your_username>.devdojo.com". My username is vnnvanhuong Everything you need to know about HTTP security headers A good collection of HTTP security-related headers. Moreover...
Post a Comment
Read more

Projects Ownership

Developers should be informed transparently about the next things that they are going to do since it impacts their mentality as well as their accountabilities. A view of Vung Tau beach First thing first, the Product Owner plays a very important role in understanding the business of the projects clearly and planning the User Stories for Development Teams. For Development Teams, we have two roles related to a project including Owner and Maintainer. The following are the definition and responsibilities for each role: Project Owner The Owner is normally assigned to the team that created the project at the beginning. It is known as the long-term project of the team. Therefore, the members of the Owner have almost knowledge of the projects including the history (i.e decisions made), business logic, and technologies used.  - Maintain a good system design (code) of the projects. Therefore, they are mandatory to review code (pull requests) from other teams. - Maintain the related documents ...
Post a Comment
Read more

Monday vhandit #2

  Introduction to OpenLDAP directory service "A directory is a specialized database specially designed for searching and browsing, in addition to supporting basic lookup and update functions" A directory service can be local, providing a restricted context; or global, providing service to a much broader context. Curlie is a good example of a directory service. LDAP (Lightweight Directory Access Protocol) is a protocol for accessing directory services , specifically X.500-based directory services. OpenLDAP is an open-source implementation of LDAP. Writing system software: code comments I have read Clean Code (by Uncle Bob) and I thought that I should void comments since the code it explains its implementation itself. That is right but not always true. In this post, the author categorized the comments into 9 types. Only "trivial comments" and "backup comments" are the ones that should be avoided. I myself agree with "writing good comments is harder tha...
Post a Comment
Read more