HI Daniel Medina,
     i just check your code and it seem that there is no function print_work_order.

so you just write a function to print the report.

And one think i noticed that in the " orden_trabajo.py"

class reporte_ot_pdf(osv.AbstractModel):
_name = "report.orden_trabajo.orden_de_trabajo"
_inherit = "report.abstract_report"
_template = "orden_trabajo.orden_de_trabajo"
_wrapped_report_class = reporte_ot

try this code.
Thanks.

Hello, thanks for your help

I modifyied my orden_trabajo.py as you said nothing seemed to change drastically, the reason why there is no print_work_order function in my module it's because I added that function on the sale's module sale.py located in models folder, I just tried deleting that function from sale's .py file and added it to my module in the file button_model.py located in the models folder

Now I'm getting the following error:

AttributeError: type object 'sale.order' has no attribute 'print_work_order'

Not sure if its a inheritance issue :(

# -*- coding: utf-8 -*-
from odoo import models, api

class boton_orden_trabajo(models.Model):
    _name = 'boton.ot'
    _inherit = 'sale.order'

    @api.multi
    def print_work_order(self):
        return self.env['report'].get_action(self, 'orden_trabajo.orden_de_trabajo')