I am new and I don't know if it is legal due to it bypassing cutscene skips etc

I have had troubles with "CFileSystem_Steam::Init() failed: failed to find steam interface" errors before which went away after I added a steam.dll to the folder. This worked for a few minutes, however, I suddenly faced a different error. I can launch portal from steam from my brother's library. But it has always been this way and so unless something has changed (in which case I will purchase the game) I have not changed anything.