Hello Natacha,

You can use Muhimbi PDF Converter for SharePoint Online for Document conversion. For details see: Muhimbi PDF Converter for SharePoint Online / Office 365 - Home  

It provides a number of option, like convert using UI, Convert using SharePoint designer and Conversion using Nintex workflows: Use Nintex Workflow for Office 365 to PDF Convert, Merge, Watermark, Secure & OCR files  

http://support.muhimbi.com/entries/88638557-About-the-PDF-Converter-for-SharePoint-Online

Hello Natache,

in addition, you can purchase additional document generation if the base 500 uses aren't enough for your scenario..contact your Nintex Partner in order to have a quote for additional use of Document Generation.

Giacomo

Thanks Giacomo Gelosi‌ Clavin Fernandes‌, but the customer can't purchase more licenses.