Acrobat DC not opening old PDF files

[Poorani_at_Avaya]

All old PDF files in our websites are not opening from the desktop nor via IE or Chrome browser.  I am using the latest Acrobat Reader DC version 19.2560.

Kindly let us know the workaround or solution as we have so many old pdf files in our doc site which cannot be redistributed.

Note: The new pdfs are opening without any issue.

Here is the error message...

on desktop:

on Chrome:

on IE:

[Bernd Alheit]

What can you see at the first lines when you open one of the files in Notepad?

[Poorani_at_Avaya]

files start with:

<?hda jcharset="UTF8" encoding="utf-8"?>

or

%PDF-1.5

[Bernd Alheit]

When it starts with

<?hda jcharset="UTF8" encoding="utf-8"?>

it is not a PDF file.

[Poorani_at_Avaya · Accepted solution]

thanks. it works when i downloaded the file again.

Also the after updating the browser versions, i am able to open the pdfs in the browser.