Hi Sambit,
Please do the follwoing:
1) Make sure that the subform/Page in which the textfield is palced is set to Flowed content. [Also, make sure that the parent of the subform in which the textfield is placed is also set to Flowed]
For eg:
<Page> - Flowed
<subform> - Flowed
<subform1> - Flowed
<textField>
2) Check the textfield property "Allow Mulitple Lines"
3) Check the textfield property "Height - Expand to fit"
4) Check the property "Allow Page Breaks within Content" of the subform in which the text field is palced
5) Most imprtant is, save your form as "Dynamic PDF".
Let me know if it works.
Thanks,
Kumar