Searching in internet, I've found the solution but not te explanation of the following error message: find: paths must precede expression: that the `find' command sometimes produces and sometimes not when used with the `*' character, e.g. to search for `*.pdf'. The solution consists in quoting the argument: '*.pdf'. But it seems to remain obscure when the error is generated and when and why not. Please, any idea? Thanks, Rodolfo