why can't I open my downloaded files?

[Android Central Question]

My phone is Oppo Android

 

[ManiacJoe]

Oppo Android

Which version of android?
Which carrier?

Which app(s) downloaded the file(s)?
Which folders are these files stored in? Internal storage or SD card?
What type of files are these?
Do you have apps that know how to read the files?
What is the exact wording of the error message you are getting?