Hello,
I encountered this when trying your latest spire presentation(10.1.1 for .net) converting a pptx slide to pdf:
Spire.Presentation.AppException: Property not found
I am unable to upload the pptx slide as it's over 3M in size, so I enclose a url to it here:
www(.)123912(.)com/s/QXV4jv-2ziCA, passcode: ZUYk
Could you please download the slide and look into it?
Thanks.