I think there are very simple solutions:

• Use the app protection from android to disable access to Markor
• Simply set the password to 123456 instead of delete the password.

Of course, those are simple solutions....and also extremely inconvenient to the point of being unusable if done 20 times a day. I already tried :).

Automation (the ideas I suggested above) removes the friction and increases security. These methods are pretty standard in most apps that deal with security, hence the request. If it's not trivial to implement any of them, I understand. I was hoping "forget while exiting" would be the easiest and most trivial option to implement.

I do say clearing / setting random password / whatever value is a easy option.
So a password input dialog triggers.

Plus some settings option, always ask for password when restarting the app (=onCreate at MainActivity). On top of that, have a delay of ~5 minutes for the restart check, so if you recently worked with Markor you don't have to re-type everytime you want to add a additional line of text.

I am using markor since last week. It is a great app. Only thing I miss is the password protection. Entire app password protection will create inconvenience. So per file password is indeed desirable.

This issue is about consuming passwords "per-file", encryption itself is already there.

You can enable it in settings. One password for all.

Yes there is an option for that, for example test.md.jenc is an encrypted file, anyone can open it from Markor, isn't it? So if anyone (e.g family members/kid) take my phone and they can see it. Am I missing something?
I thought that requiring a password to open encrypted file will be a good feature.

what you seemingly look for is more, locking Markor so you cannot use it without password.

Yes, you are right but not locking entire markor. Ask password only for encrypted file.
e.g. test.md.jenc is an encrypted file. So if i try to open it, there will be a popup dialog box which will ask for decrypt password. If i can not input correct password it will say password mismatch, otherwise open the file.