Not able to read file from server - on-premise CRM - plugins

Question

Trying to read file from server where CRM is installed. When I am reading the file from the server, plugin throws an error "Directory not found".
Entity attachment = new Entity("activitymimeattachment");
FileStream stream = File.OpenRead(fileName);
byte[] byteData = new byte[stream.Length];
stream.Read(byteData, 0, byteData.Length);
stream.Close();
// Encode the data using base64.
string encodedData = System.Convert.ToBase64String(byteData);
attachment["subject"] = "Attachment";
attachment["filename"] = "emailstatement.pdf";
//byte[] fileStream = Encoding.ASCII.GetBytes(fileName);
attachment["body"] = encodedData;
attachment["mimetype"] = #"application\pdf";
attachment["attachmentnumber"] = 1;
attachment["objectid"] = new EntityReference("email", emailguid);
attachment["objecttypecode"] = "email";
service.Create(attachment);
Can anyone help me to read file from server using plugin?
Thank you.

Answer 1

Makes sure your plugin is registered outside of the sandbox (in partial trust). Its an option in the plugin registration tool.
Plug-in isolation, trusts, and statistics
Microsoft Dynamics 365 (online & on-premises) support the execution of
plug-ins and custom workflow activities in an isolated environment. In
this isolated environment, also known as a sandbox, a plug-in or
custom activity can make use of the full power of the Microsoft
Dynamics 365 SDK to access the organization web service. Access to the
file system, system event log, certain network protocols, registry,
and more is prevented in the sandbox.