Converting Office docs into PDF (Nintex for Office 365)

For now the only way is to use the "Document Generation" action. Yes with it's support for templates with signature merging it's way more capable than a simple PDF distillery.
There are multiple requests within User Voice for adding a straight print-to-PDF action, however, it has not been picked-up by development yet.

You can use a Microsoft Flow to convert your office documents, by using the action "Convert File" in the One drive for business connector.

See : https://docs.microsoft.com/fr-fr/connectors/onedriveforbusiness/#actions

Or an exemple (first part) : http://johnliu.net/blog/2017/10/convert-sharepoint-files-to-pdf-via-flow

 

Or you can steel use Nintex and "Document Generation" to achive this task.

You stil use a predefined template, but just before using the document generation you can overwire your template with the file you want to convert (when you copy your file, rename it with the template name). 

With this solution you are able to "convert" Word to pdf but this in not an optimized solution because you can't convert multiple files at the same time, you must use sevral template for each type of documet, and you always overwirte the same template file.