Both for the testament written by yourself as well as for the testament written by someone else there are formal requirements which have to be fulfilled by all means in order to make the testament valid.
In the self-written last will it is necessary that the testator writes the entire text him/herself and signs the text at the end, so that there is no doubt regarding the testator´s identity. No witnesses are necessary for the self-written testament.
If the will is not written by hand, but by typewriter, PC or in a third person´s handwriting, you refer to it as a will written by someone else, which is subject to stricter formal requirements. The testament must be signed by the testator and must contain a handwritten amendment which points out that the document actually really contains his last will.
Furthermore, it is necessary to have the will signed by three witnesses, who have to be present at the same time, whose identity has to be clarified in the document. The witnesses merely confirm that it is the testator´s last will. In their own writing they have to point out their witness status as “requested testament witness”.
People under 18 years of age, blind people, deaf people, mute people as well as people who are not able to speak and/or understand the language in which the testament is written and so-called “biased” people cannot act as witnesses.