By default, WinEdt uses the PDF viewer which is associated with
Surely you have
.pdf files associated with Maxthon browser.
I suggest you to install the free SumatraPDF reader which works as a charm together with WinEdt. Install the 64-bit version if you have WinEdt 64-bit, otherwise install the 32-bit version.
If you want to set SumatraPDF as your default PDF reader, remember, during the installation, to click on "Options" and select "Use SumatraPDF as default PDF reader". In this case, restarting WinEdt and clicking on "PDF Preview" your
.pdf file will be opened with SumatraPDF.
If you don't want either to install SumatraPDF or to set it as your default reader, from within WinEdt, go to to "Options" -> "Execution Modes" -> "PDF Viewer" and browse for the program you want to use as PDF reader: