Step 1: First of all Navigate your default file manager settings and Check the box "Show hidden files/folder" Now Navigate to the file or folder which you want to hide in your smartphone.
To do this you Can also Download 3rd party File manager App.
Download File Expert which is the best File manager app that i personally use.
If you Use File Expert then you can just go to its setting and Tap on Show hidden files.
Step 2: Once you see the file on your Screen, Long Press it so that you can rename the file, Now just add a Dot (.) Before the file name and save it.
For Eg: if you file name is Image, Then you will rename it to .Image
Step 3: You will still be able to see that file because we have Show Hidden files/folders Enabled. so our next step is again goto file manager settings and turn off Show hidden files/folders.
Step 4: Now Navigate to the file that you renamed, You will not be able to find it because its now hidden.
How to get the file back:
To get back the hidden file you Can now again Turn on Show hidden files/folders and then rename the hidden file which will show up. just Remove the Dot that we added before the name.
Thats it your file is no longer hidden. i hope you will like this short little but useful trick. Try it yourself and let me know how it goes for you in below Comment box.