Initially I was working on win7, and now when I moved to Lubuntu 17.04, I found a series of errors. In this forum they helped me to discover that to solve it I had to update Mpdf, since the version I was using was not compatible with php 7 (although in win 7 the error never appeared to me). I'm working with php v. 7.0.22, Codeigniter v. 3.1.0. and I want to install Mpdf v. 7.0 (in windows with copy and paste folders reached, I see that in Linux you have to do a few more steps) They are new both in the development issue and in the use of linux, so in advance I apologize if I ask silly questions. Thanks for your help.