This is the root directory of the internal (emulated) sdcard
You do not have access to that directory to read a text file from there, see also the overview
Store that file in /Download and use the SAF extension to read text files, which have not been created by your own app
you can have it easy and store files in shared storage or ASD without having to ask the user
for everything else you can experiment with the SAF extension
btw. you forgot to mention where your file is coming from… did your app create it? did you copy it to the root directory using a file manager? see again the overview from my first answer…