Lock Layout of an invoice & allow filling in

I have created an invoice form which is to be completed later on by different
individuals...

Is there any way of locking the layout / structure of this invoice but still
allowing text to be inserted in the boxes??? Basically what i am trying to
prevent is the extension or minimization of the table because the invoices
will be printed on perforated sheets.

Suggestions will be highly appreciated!!!

Thanks in advance