downloading pdf via browsers appears xhtml

Hello.I notice today  when download  from  specifc  site  pdf files  from  edge  or chrome are saved to my c drive  as xhtml.This  is something  wrong?The files open correctly with acrobat  reader  but  with both of  the browsers  is  saving  with  name''xhtml''.Is  something about  the site?(is under upgrading).It something about  the two browsers?I tested  with other sites  and the  download pdf files appears  as...pdf.....

So  what  about?And what is xhtml?