If you’re viewing a large (file-size) PDF in Firefox, you might occasionally get an error message saying “The file is damaged and could not be repaired.” However, if you try to open the PDF in Internet Explorer or save the file to the desktop and open it in Adobe Reader it works just fine. This fact causes you to doubt the validity of the message you’re receiving in Firefox, as it should. There is nothing wrong with the file and it seems to be isolated to opening the PDF in Firefox.
I have resolved the problem once before by copying the plug-in file (C:program filesMozilla Firefoxpluginsnppdf32.dll) from a working computer to the problematic problem. If you were to uninstall and reinstall Adobe Reader, this plug-in would be removed and replaced in the process. In my latest encounter with this problem, uninstalling Adobe Reader and installing the latest version didn’t resolve the problem nor did updating Firefox.
I was able to find the solution, however, in a user misconfiguration. In Firefox, if you go to Tools, Options… it will pull up a new window for Options. Switch to the Advanced ‘tab’ and then under that the Network tab. You’ll see a setting for Offline Storage: Use up to __ MB of space for the cache. The default size for the cache is 50 MB. When I investigated, the user was configured to only use 10 MB for cache and since the PDF was approaching this limit in size, apparently it couldn’t download the entire PDF. Adobe Reader then, with only part of a PDF file, determined that the file was damaged beyond repair.
Either restore the Offline Storage to the default 50 MB size or increase it to a higher, yet reasonable number if you’re dealing with files larger than or approaching 50 MB. Hit the ‘Clear Now’ button to clear the cache and hit the ‘Ok’ button for the setting to be saved. You should now be able to open the PDF in Firefox. If it still doesn’t work, close and re-open Firefox. Then attempt to open the PDF.
Ta-dah! Now, after adjusting the setting, the PDF is viewable inside Firefox again!