The variable fullpath is a string already. When you use 'fullpath' in quotes, that's passing the string "fullpath" to load. Remove the quotes to pass the variable to a function. But load() expects a .mat file, or "an ASCII file containing numeric data with same number of columns in each row." If your file is formatted like that, fantastic. Otherwise, you might need something else.
readmatrix() or importdata() will load, e.g., a csv file.
If it's pure text, readlines() might work.
