Hi Leszek,
Thank you for contacting Syncfusion support.
Yes, we support flow layout rendering in PDF document in UWP platform by using PdfTextElement and PdfLayoutResult instances. we have created a simple sample for creating a flow layout by using PdfTextElement and PdfLayoutResult for your reference, please refer the below sample for more details.
Please let us know if you have any concern.
Regards,
Chinnu