Is there a way to control those margins, to set them to 0?
No, there is not an option right now. Though you could post-process the PDF file, and shrink the page size, by adjusting the CropBox.
https://www.pdftron.com/api/ios/Classes/PTPage.html#/c:objc(cs)PTPage(im)SetCropBox:
PTPage.GetVisibleContentBox might be useful here, see this forum post.
https://www.pdftron.com/api/ios/Classes/PTPage.html#/c:objc(cs)PTPage(im)GetVisibleContentBox
If the above does not answer your question, why is having no margin important for you?
I’m also interested in paperSize parameter that is forwarded to the conversion method. I can read the width and height of the slide in original file, but I’m not sure how those (EMU) values convert to the expected values that the method consumes.
The paperSize paramater is in PDF units which are 1/72 inch. If you can determine the physical dimensions of the EMU values then you can convert to the PDF units using the 1/72 inch scale.