PDFKit issue with PDFs created by CoralDRAW

We are using PDFKit framework to display PDF and add annotation on PDF files. Before rendering PDF for the display we are using PDFKit framework's write method to save the PDF file in documents directory. It supports most of the functionality required for our application but for few PDF files we are not able to recognize text on PDF. To those PDF files we are unable to search keyword. After lot of research we found out that the issue is occurring for PDF files which are created via CorelDRAW. We are requesting your assistance in this issue as lot of our users are creating PDFs via CoralDraw software. Please let me know in case of more clarification.