Requirement:

Customer has saved some JSON files in local folder of laptop or server or drive. Customer wants upload the JSON files from local drive to microsoft Dynamics 365 finance and operations for further business process. A dialog will open in Microsoft D365 fin & ops, customer will select JSON files and import.

Sample Code:

public static void main(Args _args)
{
str jsonString;
FileUploadTemporaryStorageResult fileUpload = File::GetFileFromUser() as FileUploadTemporaryStorageResult;
System.IO.Stream stream = fileUpload.openResult();
using (var reader = new System.IO.StreamReader(stream))
{
jsonString = reader.ReadToEnd();
}