Loading a .txt file into a blob

I want to load a .txt file into NAV, so i can store it later in a BLOB field in a table. tried this:

FileManagement.BLOBImportFromServerFile(TempBlob, FileName);

Where FileManagement is Codeunit 419
TempBlob is Record from TempBlob table
And FileName is acquired by choosing it from a dialog window earlier, so looks like: C:/Users/username/Desktop/myFile.txt

I get an Error "File does not exist" when clearly it does at that path, so maybe I'm doing something wrong
NAV 2017