@CØK Can you please share the document that you are trying to open.Also please share details , how its created.If you have a template file and data file which were used to merge and create the PDF, please share that as well.  

You can go to location C:\Users\username\AppData\Roaming\Adobe\Designer\6.5 as mentioned by @radzmar  and share file InspectorsEN193.xml with any other user to import your UI settings.The user should replace existing file with the new one and then open the designer to see customized UI

Hello @CØK We would need more data to analyse the cause of this issue.If you can share the template file and the config file (xci) used here to create the PDF, that would be helpful.