Hello, @gilles. Thanks for reaching out.
If you need to convert a single page, there are a few ways for you to get rid of the black background:
- place the content you want to convert into the group and convert this element into the PDF file (with the specific conditions, set in the workflow);
- convert the whole page into the PDF, with the specific conditions in the workflow.
In a case for the element conversion:
Portrait orientation > elment size (for example) are 960x1080:
- you need to add 15/30 px more to the target/source format values (width/height), than your current element has;
- uncheck the Breack content into pages checkbox;
- use only the Custom Format (target/source);
 design-1, design-2, workflow-1, workflow-2, preview, result PDF.
Landscape orientation > element size (for example) are 1080x960:
- all the same settings, as for the portrait, but swap the width and height.
In a case for page conversion:
Portrait orientation:
- you need to add 15/30 px more to the target/source format values (width/height), than your current element has;
- uncheck the Breack content into pages checkbox;
- Source Format - Custom;
- Target Format - a4;
 design (the same), workflow-1, workflow-2, preview (the same), result PDF.
 Landscape orientation:
- all the same settings, as for the portrait, but swap the width and height (Source Format).
I hope this will help you 
Regards,
Zeroqode Team