Here's the response from Eltima Tech Support
'Please note that Folx requires a direct link to the file in order to
download it. In this case the link you used is to Google's search
results, that's why Folx is not able to download it, as it is not a link
to the file. In order to download this image with Folx, you need to
right-click on the image, choose 'Copy Image Location' option and then
paste it into “Quick Add” dialog of Folx.
The thing is that this link is not a direct link to the PDF file, too.
It is the link to the website
Archaeology Data Service,
that's why Folx can not download the required file. If you open the
downloaded file with TextEdit, then you will see that Folx downloaded an
html file of this website home page.
Also, I'd like to draw your attention to the fact that Folx GO doesn't
feature downloading videos from Youtube due to the MAS restrictions.
Please, see the description here:
Folx
YouTube downloads are supported with the PRO version of Folx that we
distributed through our website. You can find more information about it
here:
Folx: Free Download Manager for Mac
If you need to download videos from Youtube, I can offer you a 50%
discount on a license for the Folx PRO version, if you send me a
screenshot from your Purchase History confirming Folx GO purchase.” Kate Gardner
Outlook – free personal email and calendar from Microsoft