Do something like this:
folder = pwd;
absoluteFileName = fullfile(folder, relativePath, baseFileName);
where folder is the current folder, say 'C:\users\Razvan\Documents' or whatever other folder you want. relativePath is something like '\subFolder1\subfolder2', and baseFileName is something like 'myData.txt'. So the final folder would be 'C:\users\Razvan\Documents\subFolder1\subfolder2\myData.txt'. fullfile() takes care of figuring out whether to use forward or backslashes and making sure that you don't have two of them when the strings are concatenated.