When I try and install apk file by clicking from Files App, I get the error message "Cannot display pdf (.apk is of invalid format.)"

The system tries and opens pdf reader app, instead of package installer app.

When trying to install from Downloads App, I get the message "can't open file".

The phone is a new OnePlus X phone with OxygenOS 2.2.1, Android Version 5.1.1

In the Settings, I have checked the Unknown Sources App Installation Option.

Also I cannot see the Developers Option in Settings.


The developer options become available after you click the build number 7 times in the about section of your phone.

  • Thanks you for this. I figured that out later. However I am still stuck with the installation problem. Is there some place in android where you can associate file names with what applications open them?? – user2007547 Apr 30 '16 at 19:47

Referance: Your apk file is not named correctly and thats the problem here. if your apk name is like app apk or app_apk then its possibly causing the problem.

Solution :

  1. Download any good file explorer ( i recomend es explorer/solid explorer/fx filemanager but any good solid file manager will work).

  2. find the file and rename it with an .apk at end.

  3. install app as you used to do :)

  • Thanks for the answer but I left out the name of the apk in the question deliberately. It is correctly named. – user2007547 Apr 30 '16 at 19:46

Download and install ES file explorer from the play store. It should identify the file correctly.

Another solution would be to connect the device in debug mode and use

adb install filename.apk

to get the apk installed. You however need to have adb setup on your computer to use this method.you can find adb in the Android SDK by Google or search for and download a standalone minimal adb.

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