Thanks to you all.

With  your suggestion I could solve my problem.

Riccardo

Thank you so much for your support.

PAGAN
I need to change the name before importing the file. What I'm loking for is a way to automate my process as I have to repeat it for many set of 50 files each. That is, to change the name of the files in the form 1.txt..50 txt automatically, in the directory, indipendent from the namefile I choose when i record the data. 

PREBEN
The rename tool it is not very flexible for my use, as it requires that i change the name of each file individually and I have to work with many set of 50 files each.

Thank you again