Hi Mehregan,
you can find the url by going to MEDIA and clicking on a PDF file:
[image: 0_1534317134776_Bildschirmfoto 2018-08-15 um 09.11.56.png]
[image: 0_1534317162208_Bildschirmfoto 2018-08-15 um 09.11.59.png]
That is the URL.
Hope I could help!
Marius