Check if folder exists and collect shared folder

Thank you again Steve , you are great . So my solution for the first question was something like this:

private bool CheckIfCloudPathExists(string cloudPath)
{
Metadata metadata = new Metadata();
try
{
System.Threading.Tasks.Task<Metadata> taskUpload = Task.Run(() => GetFolderMetadata(cloudPath));
if (taskUpload.Result != null)
metadata = taskUpload.Result;
}
catch (AggregateException e)
{
if (e != null && e.InnerException != null && e.InnerException is ApiException<GetMetadataError>)
{
GetMetadataError err = (e.InnerException as ApiException<GetMetadataError>).ErrorResponse;
if (err.IsNotFound || err.IsOther)
return false;
}
}
return metadata != null;
}

I will reformulate the second question : Is it possible to set permisions to a file like this :

File cloudFile = GetCloudFile(CloudPath); //here I'm getting my file ,and then I set it's permissions
if (cloudFile == null)
return false;

Permission newPermission = new Permission();
newPermission.Value = UserEmail;
newPermission.Type = "user";

if ( PermissionType == 1 )
newPermission.Role = "reader";
else if (PermissionType == 2)
newPermission.Role = "writer";

try
{
PermissionsResource.InsertRequest insertRequest = GoogleDriveService.Permissions.Insert(newPermission, cloudFile.Id);

if (NotifyUserByEmail == false && UserEmail.EndsWith("@google.com"))
insertRequest.SendNotificationEmails = true;
else
insertRequest.SendNotificationEmails = NotifyUserByEmail;

if (!string.IsNullOrEmpty(OptionalEmailMessage))
insertRequest.EmailMessage = OptionalEmailMessage;

var retVal = insertRequest.Execute();
}

This example is made on google api . When I want to share a file , I set it's permissions.