What happens when you download a PDF that then refuses to load, or you open a video only to find it won't play? Being unable to open files as usual is one of the most frustrating tech problems you're likely to encounter. But you shouldn't give up and delete them right away. Most of the time, the following tricks will let you fix the issue yourself.
Find the cause
All kinds of problems could be making that file refuse to open. Maybe the file has become corrupted, or someone saved it in an incorrect format, or you're simply opening it with the wrong program. A bit of detective work at the beginning can help you work out what the problem is. From there, you can choose the best way to solve it.
If you're not sure what kind of file you're dealing with, a couple of online tools can help. CheckFileType and Online TrID File Identifier both let you upload a file in your browser and then identify the mystery item. Once you know the file type, you can find a program capable of accessing it. As always, be wary of opening files you aren't sure about or that have come from suspicious sources.