Context and Problem Statement🔗
How can office documents, like
odt be converted into a PDF
file that looks as much as possible like the original?
It would be nice to have a java-only solution. But if an external tool has a better outcome, then an external tool is fine, too.
Since Docspell is free software, the tools must also be free.
- Apache POI together with this library
- pandoc external command
- abiword external command
- Unoconv external command
To choose an option, some documents are converted to pdf and compared.
Only the formats
odt are considered here. These are the
most used formats. They have to look well, if a
doesn't look so great, that is ok.
Here is the native view to compare with:
I couldn't get any example to work. There were exceptions:
java.lang.IllegalArgumentException: Value for parameter 'id' was out of bounds at org.apache.poi.util.IdentifierManager.reserve(IdentifierManager.java:80) at org.apache.poi.xwpf.usermodel.XWPFRun.<init>(XWPFRun.java:101) at org.apache.poi.xwpf.usermodel.XWPFRun.<init>(XWPFRun.java:146) at org.apache.poi.xwpf.usermodel.XWPFParagraph.buildRunsInOrderFromXml(XWPFParagraph.java:135) at org.apache.poi.xwpf.usermodel.XWPFParagraph.<init>(XWPFParagraph.java:88) at org.apache.poi.xwpf.usermodel.XWPFDocument.onDocumentRead(XWPFDocument.java:147) at org.apache.poi.POIXMLDocument.load(POIXMLDocument.java:159) at org.apache.poi.xwpf.usermodel.XWPFDocument.<init>(XWPFDocument.java:124) at docspell.convert.Testing$.withPoi(Testing.scala:17) at docspell.convert.Testing$.$anonfun$run$1(Testing.scala:12) at cats.effect.internals.IORunLoop$.cats$effect$internals$IORunLoop$$loop(IORunLoop.scala:87) at cats.effect.internals.IORunLoop$RestartCallback.signal(IORunLoop.scala:355) at cats.effect.internals.IORunLoop$RestartCallback.apply(IORunLoop.scala:376) at cats.effect.internals.IORunLoop$RestartCallback.apply(IORunLoop.scala:316) at cats.effect.internals.IOShift$Tick.run(IOShift.scala:36) at cats.effect.internals.PoolUtils$$anon$2$$anon$3.run(PoolUtils.scala:51) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748)
The project (not Apache Poi, the other) seems unmaintained. I could not find any website and the artifact in maven central is from 2016.
I know pandoc as a very great tool when converting between markup
documents. So this tries it with office documents. It supports
odt from there
From the pandoc manual:
By default, pandoc will use LaTeX to create the PDF, which requires that a LaTeX engine be installed (see --pdf-engine below). Alternatively, pandoc can use ConTeXt, roff ms, or HTML as an intermediate format. To do this, specify an output file with a .pdf extension, as before, but add the --pdf-engine option or -t context, -t html, or -t ms to the command line. The tool used to generate the PDF from the intermediate format may be specified using --pdf-engine.
Trying with latex engine:
pandoc -f odt -o test.pdf example.odt
pandoc -f odt -o test.pdf example.docx
Trying with context engine:
pandoc -f odt -t context -o test.pdf example.odt
Trying with ms engine:
pandoc -f odt -t ms -o test.pdf example.odt
Trying with html engine (this requires
wkhtmltopdf to be present):
$ pandoc --extract-media . -f odt -t html -o test.pdf example.odt
abiword --to=pdf example.odt
Trying with a
docx file failed. It worked with a
Unoconv relies on libreoffice/openoffice, so installing it will result in installing parts of libreoffice, which is a very large dependency.
unoconv -f pdf example.odt
The results from
unoconv are really good.
Abiword also is not that bad, it didn't convert the chart, but all font markup is there. It would be great to not depend on something as big as libreoffice, but the results are so much better.
Also pandoc deals very well with DOCX files (using the
engine). The only thing that was not rendered was the embedded chart
(like abiword). But all images and font styling was present.
It will be a configurable external command anyways, so users can exchange it at any time with a different one.