How to increase visual length of form text field in Word?

Solution 1:

Within the "properties" window (after right-clicking on the field), there is a default text option. If you insert spaces there, the size of the field shown will grow to compensate. The more you need to grow the field visibly, the more spaces should be added to the default text field.

Solution 2:

The grey shading is just to indicate there is a form field there. By default the field will hold unlimited text, unless you change the field properties to only be a certain length. Still, the shading will only show a few spaces until you type, then the shading grows as you continue type.

As far as I know, there is no way to extend the shading when there is no text in the field. If the field is in a table, you could shade the entire cell.

Solution 3:

If you have at least one Asian language pack installed you can "stretch" the form field by using Distributed text alignment. From there you can choose the width and if you set this to a higher value it will expand the form field as well.