Manual mo palitan kung paano maopen mga files mo. Tignan mo din file extensions
.pdf maoopen ito ng application like adobe reader / sumatra pdf
.docx maoopen ito ng application like MS Word / writer
.rar / .zip / .7zip maoopen ito ng application winrar / 7zip / winzip
Para makita file extensions
open mo folder option > view tab > untick mo Hide extension for know file types