The only operations that can be present in a "function" line are:
 -- around the list of output variables only, no-where else on the line
() -- around the list of input variables only, no-where else on the line
comma -- separate the list of input variables and list of output variables
~ -- replacing one of the input variables, indicating it should be ignored
Calculations and indexing of all varieties are not permitted.
In particular it is never valid to have a quoted string in the function line.
Your code should look like
function [output] = calculate_tfidf(filename)
output = load(filename);
and you should invoke it like
output = calculated_tfidf('E:\backup\Media\collection1.txt');