Hi,
Would you please help us with the following queries?
1. When you say 'writing on it', do you mean you are adding a freehand drawing/ink signature to the form or filling out the form fields?
2. After emailing the document, while opening it, are you opening the form in Adobe Reader on Android?
3. If you don't email the document and just close it after filling it or writing on it, do you get a 'Document saved' toast? On reopening the file, are your edits visible?
Please let us know of the exact steps you are following along with the android version and device details so that we may resolve the issue.
Thanks,
Adobe Reader Team