TFile f("sub.root", "RECREATE");
TCanvas c("c", "c");
TH1F h("h", "h", 100, 0, 1);
h.FillRandom("gaus");
h.Draw();
c.Write();
f.mkdir("subd");
f.cd("subd");
TCanvas c2("c2", "c2");
TH1F h2("h2", "h2", 100, 0, 1);
h2.FillRandom("gaus");
h2.Draw();
c2.Write();
f.Write();
f.Close();

rootprint -vr sub.root 
Info in <TCanvas::Print>: pdf file c.pdf has been created
Info in <TCanvas::Print>: pdf file subd_c2.pdf has been created
Info in <TCanvas::Print>: pdf file h.pdf has been created
Info in <TCanvas::Print>: pdf file subd_h2.pdf has been created
rootprint -v sub.root 
Info in <TCanvas::Print>: pdf file c.pdf has been created
Info in <TCanvas::Print>: pdf file h.pdf has been created