LibreOffice - Force PDF/A export

I was using LibreOffice to convert documents from disparate formats to PDF. This is done by using the following command:

libreoffice5.3 --headless --convert-to pdf prueba.txt

My problem was that the output file was not int PDF/A format.

LibreOffice, by working with it´s GUI interface, do supports PDF/A conversion, so the problem should be in some kind of default configuration.

There is configuration file called registrymodifications.xcu which contains all settings used by the programa, and during the exportation too. This file is located in  ~/.config/libreoffice/4/user/ directory. For example /root/.config/libreoffice/4/user/registrymodifications.xcu.

This is an xml based file with a lot of (poor/undocumented) preferences. In particular, in order to set PDF/A as default option, you have to insert the following config line:

<?xml version="1.0" encoding="UTF-8"?>
<oor:items xmlns:oor="http://openoffice.org/2001/registry" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 (...)
 <item oor:path="/org.openoffice.Office.Common/Filter/PDF/Export">
  <prop oor:name="SelectPdfVersion" oor:op="fuse">
   <value>1</value>
  </prop>
 </item>
 (...)
</oor:items>

Now, if you launch the conversion again you will get a PDF/A-1A file.

Though registrymodifications.xcu file is quite obscure, you can get mor info by using the GUI version of the program. If you navigate to Tools > Options > LibreOffice > Advanced > Open Expert Configuration, you can check the whole list of settings.