IPhone :: Create A Password Protected File?

I've been trying to find a way to create a password protected file that I can use on my iphone and ipad for sensitive information. I've tried the password protection on Pages for mac, but once the file is opened in Pages on IOS, there's no way to close it.So, now I think I have a solution by creating a pdf file and adding a password to it, using Preview on mac.

1. create a file using textedit, and Export to pdf.

2. open that pdf in Preview and Export to pdf, with a password.

3. add this encrypted file to the iTunes library.

4. sync the iphone / ipad

5. use iBooks on the IOS to open the file. It will ask for the password. To close, the file, quit the iBooks App.

It looks like this meets my needs. BTW, if you're using windows instead of the mac, you can install libreoffice and use it to create the password protected pdf, then just add it to iTunes and sync the iphone. So, my question is for those who know the inner workings of the mac and IOS, and is whether this is actually secure or is this file crackable?

Info:
iPhone 4, iOS 5