PDF file is damaged and cannot be restored, but the browser opens.

Hello everyone. As you can see from the topic, that's the problem. The browser opens any: IE, chrome, Mozilla.
Adobe Acrobat X v. 10.1.10.18 (updated today)
Windows 7 ultimate SP1
I opened files. The part from them still opens. And I somehow took the old file and decided to open - but in any way. Well I it again from the site downloaded. Again mistake. But if the browser is open then everything is OK.
Any ideas?

See a similar question on this forum
http://www.filerepairforum.com/foru...to-open-corrupted-when-downloading-a-pdf-file
If "Not open" - then DblClick or via the menu File > Open?
And what about action of its license? If to make other user on the computer? what will be in a profile of this other user? You can still try to restore the file via the utility of Recovery Toolbox for PDF. It well restores PDF files. https://pdf.recoverytoolbox.com/

I don't know about Chrome or IE, but Mozilla is crying wolf about Adobe's Flash and PDF Reader and will attempt to use its built-in half baked attempts.
In the case of Mozilla, go to preferences, then 'Applications'.
There, scroll down until you see 'Portable Document Format' and from the right-hand side list choose Adobe's plugin.
If they are indeed insecure - sorry but there's no telling how dangerous in your use cases.