Truecrypt: is it possible to add a "keyfile" to a already "passworded volume" ?

I have several truecrypt volumes which I have created with passwords only.
For an added security I wanted to add a keyfile to all of them

if I do it, would I be able to open it in android phone with which software

 

If you want added encryption, use Veracrypt. It uses iterations.

 

You can simply add a keyfile to a volume, data currently on the volume will not be lost.
(Changing of the password or adding of a keyfile only affects the Volume Header)

First select a volume, then use the option: "Volumes -> Add/Remove Keyfiles to/from Volume".
In the next dialog you can select a keyfile which you want to add to the volume.

 

I have just did it through your instructions successfully.
I appreciate your help very much. Thank you.

 

You're welcome