@Thomas Richard Ah, ok, I don't know it have to be used together with "assume". I will try to adapt my code with this new instructions. Thank you very much!!

@Thomas Richard Thank you for your answer. But this doen't work for variables, I think. For example sqrt(x)

@Rouben Rostamian  

Thank you. I had tried this before, but I still don't get the expression I see in the output. I don't know how to upload a file, so I copy here a simple code:

restart; 
with(DifferentialGeometry); 
DGsetup([x1, x2, x3, x4], M); 
w := evalDG(dx1*x1+dx2*x3); 
latex(w)

The output is

but if I copy and paste I get:

         _DG([["form", M, 1], [[[1], x1], [[2], x3]]])
{\it x1}\, DifferentialGeometry:-TeXFormList[M][1]+{\it x3}\, DifferentialGeometry:-TeXFormList[M][2]

Thank you very much for your time!