Thanks for your inquiry. Sorry that our Spire.PDFViewer doesn't have the capacity to allow user to copy the contents manually while viewing. If you have other questions, welcome to write back.
Is there currently a workaround you could share with us? I'm having the same customer requirement, a user wants to copy text from the PDFViewer / PDFDocumentViewer.
Thanks for your feedback. Sorry, at present there is no workaround. We have added it as a new feature into our upgrade list. Once the new feature is available, we will let you know.