Texmaker does not edit pdf file

I am new to LaTeX and using Texmaker. The changes I’ve made were successfully saved in a tex file. I see them in Texmaker, but the pdf didn’t change. The problem is not in the pdf viewer because when I open the pdf by itself I cannot see any changes made. I didn’t get involved in the work at start and a lot of work had already been done before me. There was no such problems before.