Cannot edit fill and sign elements between use sessions

Hello.

I open a PDF in Acrobat Reader Mobile and use the FIll and Sign tools but don't technically sign the document. I close the document to do something else and with the original Adobe FIll and Sign app I could reopen that same document and edit a text field that I added, for example.

However, in Acrobat Reader Mobile the text box cannot be edited after reopening the document.

What am I doing wrong?

Thanks
Morgs