Thank you for contacting support. It is due to the evaluation limitations. You’ll also find an evaluation watermark in the output PDF. You can discard these limitations by applying a valid Aspose license. You can get a 30 day temporary license for the testing purposes from the purchase portal. Its option is available in step 4. In case, this does not work, then please register a thread in the Aspose.Purchase forum.
Please also refer to this help topic: How to Apply the Aspose License
Please let us know in case of any confusion or questions.