Hi Paw,
Thank you for your interest in Syncfusion products.
The Version 5.2 of Essential PDF is a complete rewrite, so the APIs are not compatible with the previous version of Essential PDF. For applications that use all previous versions of Essential PDF, please refer Syncfusion.Pdf.Legacy.Base.dll which is included with v5.2 for maintaining compatibility and your application should work without any problem. We recommend using new library for any new development work since it will be actively supported and enhanced. We regret for the inconvenience caused.
Please refer release notes for more info.
http://www2.syncfusion.com/installs/v5.2.0.25/release_notes/ReleaseNotes.htmPlease let me know if you have any other queries.
Regards,
Jaya