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When we create the pdf document in multithreading we need to make disable the following property to avoid reported exception.
PdfDocument.EnableCache = false;
The sample project is attached for your reference.
Please let us know if you need further assistance.
We were able to reproduce the problem and have logged defect report regarding this. A support incident to track the status of this defect has been created under your account. Please log on to our support website to check for further updates
Please let me know if you have any questions.
Sorry for the inconvenience caused.
Could please check your account for the incident now?