---
layout: docs
title: Convert Office Documents
permalink: dev/adr/0009_convert_office_docs
---

# {{ page.title }}

## Context and Problem Statement

How can office documents, like `docx` or `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.

## Considered Options

* [Apache POI](https://poi.apache.org) together with
  [this](https://search.maven.org/artifact/fr.opensagres.xdocreport/org.apache.poi.xwpf.converter.pdf/1.0.6/jar)
  library
* [pandoc](https://pandoc.org/) external command
* [abiword]() external command
* [Unoconv](https://github.com/unoconv/unoconv) external command

To choose an option, some documents are converted to pdf and compared.
Only the formats `docx` and `odt` are considered here. These are the
most used formats. They have to look well, if a `xlsx` or `pptx`
doesn't look so great, that is ok.

Here is the native view to compare with:

ODT:

<div class="thumbnail">
  <img src="./img/example-odt-native.jpg" title="Native view of an ODT example file">
</div>

### `XWPFConverter`

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.


### Pandoc

I know pandoc as a very great tool when converting between markup
documents. So this tries it with office documents. It supports `docx`
and `odt` from there `--list-input-formats`.

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
```

Results ODT:

<div class="thumbnail">
  <img src="./img/example-odt-pandoc-latex.jpg" title="Pandoc (Latex) ODT->PDF">
</div>


```
pandoc -f odt -o test.pdf example.docx
```

Results DOCX:

<div class="thumbnail">
  <img src="./img/example-docx-pandoc-latex.jpg" title="Pandoc (Latex) DOCX->PDF">
</div>


----

Trying with context engine:

```
pandoc -f odt -t context -o test.pdf example.odt
```

Results ODT:

<div class="thumbnail">
  <img src="./img/example-odt-pandoc-context.jpg" title="Pandoc (Context) ODT->PDF">
</div>


Results DOCX:

<div class="thumbnail">
  <img src="./img/example-docx-pandoc-context.jpg" title="Pandoc (Context) DOCX->PDF">
</div>


----

Trying with ms engine:

```
pandoc -f odt -t ms -o test.pdf example.odt
```

Results ODT:

<div class="thumbnail">
  <img src="./img/example-odt-pandoc-ms.jpg" title="Pandoc (MS) ODT->PDF">
</div>

Results DOCX:

<div class="thumbnail">
  <img src="./img/example-docx-pandoc-ms.jpg" title="Pandoc (MS) DOCX->PDF">
</div>


---

Trying with html engine (this requires `wkhtmltopdf` to be present):

```
$ pandoc --extract-media . -f odt -t html -o test.pdf example.odt
```

Results ODT:

<div class="thumbnail">
  <img src="./img/example-odt-pandoc-html.jpg" title="Pandoc (html) ODT->PDF">
</div>

Results DOCX:

<div class="thumbnail">
  <img src="./img/example-docx-pandoc-html.jpg" title="Pandoc (html) DOCX->PDF">
</div>


### Abiword

Trying with:

```
abiword --to=pdf example.odt
```

Results:

<div class="thumbnail">
  <img src="./img/example-odt-abiword.jpg" title="Abiword ODT->PDF">
</div>


Trying with a `docx` file failed. It worked with a `doc` file.


### Unoconv

Unoconv relies on libreoffice/openoffice, so installing it will result
in installing parts of libreoffice, which is a very large dependency.

Trying with:

```
unoconv -f pdf example.odt
```

Results ODT:

<div class="thumbnail">
  <img src="./img/example-odt-unoconv.jpg" title="Unoconv ODT->PDF">
</div>

Results DOCX:

<div class="thumbnail">
  <img src="./img/example-docx-unoconv.jpg" title="Unoconv ODT->PDF">
</div>

## Decision Outcome

Unoconv.

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 `context`
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.