You cannot change the sizes of the formfields, though you can put them into table cells of fixed row height & column width to constrain their line length & count - or you could use multiple formfields (eg one per line).

An alternative, if it suits your purpose, would be to use just the table. With Section breaks either side of the table, you could leave the table's Section unprotected. The only risk with that approach is that users might use Word's table tools to resize the table.

Aside from the above re using only a table, it and any formfields you insert will stay put and the users can save as PDF. There will be no formfields in the PDF - just their content.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]