Question Problem with PDF attachments

ha sorry my mistake i had the j3. overlooked
now i see the correct forum with attachment
have you tried it with another pdf? and there are no spaces in the filename?
and in Kunena Forum: Configuration>tab uploads>Protect Attachments is set to no ?
 

You have enabled attachment protection in the configuration (Attachments tab), which may cause problems with PDFs. Please try it with disabled protection.

The Protect Attachments setting has no effect.
However, the presence of spaces in the pdf filename is the problem. And that's a problem - because we can't control filenames that people may have for their attachments.
It's very odd that this problem exists only for pdf filenames. The other samples on the test site (docx, xlsx, and txt files) all have spaces in the filenames yet work as expected.

it can't be the case that the name of the pdf(...red Miners) activates your website protection?
the ... is that also part of the file name if you remove those 3 dots does that pdf work? activate your website protection ?

I very much doubt that's the problem. The shortened filename that appears is governed by the configuration setting (in the Frontend tab) for "Number of characters from end for shorten filename". It's doing the same thing for each of the other filetype attachments in my post on the test site. And there's nothing in that filename - or in the filenames of the attachments in the post on the real site that alerted us to this problem - that would trigger our custom URL protection.

 I find it strange that I can choose all attachments what I want to do with it save or read in browsers so also the last one posted Sample_PDF_File.pdf
Except those red miners.pdf
I'm going to think that the file is damaged or incorrectly uploaded, the more so because I don't even inspect file name (numbers and letters only). (as I can see at sample_pdf)
or other way the file itself is somehow secured.