Thank you for contacting Syncfusion support.
We have checked the reported margin issue, but it is properly set to zero when creating PDF document. We have attached a simple sample, which creates PDF document with zero margin and draw the text in top left of the page. It does not adds any margin in the created document. Please find the sample and output document from below link,
Kindly try the above sample and let us know the result, if still you are facing the same problem, kindly share us the complete code snippet and output PDF document to us. This will be helpful for us to analyze and assist you further on this.