The font size in PDF form field text box become small when the text length is too long

We are used Aspose.pdf 24.11.0, after fill form field text box, the font size become small when the text length is long, even we have set the font size to 9 in pdf template. We don’t want the aspose to change font size. How can we do it?
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@Venus_Huang
We are looking into your question and will respond soon.

@Venus_Huang
You did not attach the document (and the code used). Therefore, I will write hypothetically.
Probably, the input field is set to auto-select the font size.
To check this, you can open the document in Acrobat (I am not sure about other viewers) and see if the font size changes when entering a different number of characters.
If so, you can set a fixed font size for the field:

Field.DefaultAppearance = new DefaultAppearance("Arial", 14, System.Drawing.Color.Blue);