I must migrate from one page to another and the customer want me to keep the password. But as their are im MD5 and salted, I don't know how to proceed. Does anyone know it? Thank you a lot for your help.
You can't. Wordpress stores the passwords in the DB as hashes of the user password using a salt which is unique to the install. In an import situation (unlike full migration) you will probably not have the same salts in the new site and password validation will fail.
You should just notify the users that they should reset their password.
Migrating WordPress users with their password is easily possible with this WordPress user import export plugin.