Sorry, i have forgot about it: "WinHTTrack Website Copier 3.41-2".

> I assume you have options -> Links -> Get non-HTML = 
> checked or added +*.pdf
> in the filters.

Yes, both options. The links aren't inside any javascript.
For example, this page:
<http://www.megasensor.com/product_info.php/products_id/609>

Max. download rate: 50000
Some additional filters, like +*.pdf
Get non-HTML = checked

As i said, all links in the source code to the external files are the same,
because they are generazed automatically and have no abnormal escapes or some
thing else. I don't see any regularity... :(