ROOT creates PDF that appear different than PNG

Greetings,

I am curious to know how to get my PDF file output to look like the PNG file output.

I am attaching both outputs.

They both are created from the same histogram, within the same macro. The method of creating them is by saving a TCanvas i.e.

c1->Print("prot_theta_p_TOFKnockout_sec3.pdf")
c1->Print("prot_theta_p_TOFKnockout_sec3.png")

Notice that in the PDF output, the X axis titles are drastically different from the PNG version.
How to I get my output of the PDF to appear as the output of the PNG?
BR
MK

prot_theta_p_TOFKnockout_sec3.pdf (237 KB)