How does one, edit text using Preview?

Hi all,

I have recently created a document using Preview...The document includes text that I inserted using the text tool within Preview itself...I was able to edit these text windows quite freely during the creation of the document...

However, today I have opened my Preview document only to find that the usual method of clicking on the text is failing and that I cannot edit those very same text windows anymore...How is this so and how can I edit them once again?

Any help muchly appreciated, thank you!

Regards,

Brad