We observed that you have updated reviewer rights in only UpdateCollaborator method but the error was generated in ManageCollaboratorRights, please update reviewer rights in this method as well. Also, comment below code line under #region Annotation Functions for Slides in Program.cs class in order to avoid Cannot open pdf file error
CommonUtilities.filePath = "sample.pptx";
With above changes we are unable to reproduce these issues at our end. Moreover, we will recommend you to evaluate examples one by one and for your ease, we do have documentation for developer. Please go through the wiki and let us know if your issues are resolved.