Issue of changed font after changing field text of widget

[zergb]

Hi,
I'm using PyMuPDF to fill a PDF form. My expectation is to update only the values within text fields, leaving the original font formatting intact. However, the font is changing unexpectedly. For instance, original font Arial Bold is being replaced with default font Helvetica. When I make the same changes in Adobe Acrobat, the font Arial Bold is preserved correctly. My code is attached below. I'd appreciate any insights into how to resolve this issue. Thanks in advance!

def main():
    fn = "form.pdf"
    doc = pymupdf.open(fn)
    page = doc[0]
    for widget in page.widgets():
        widget.field_value = "Filled Text"
        widget.update()
    doc.save(fn+".pdf")
    doc.close()

[JorjMcKie]

(Py-)MuPDF currently only supports Helvetica, Times-Roman and Courier in text widgets - no bold, no italic.
This will change in a future version, but currently nothing can be done about this.

Independent from this:
If you change a widget created by some other software, you will generally change the widget completely - not only the property you intended.
This is true across all PDF products: changing an Adobe-created widget with Nitro PDF will completely recreate it.

[zergb]

Thank you for your explanation. I understand the reason for the problem. This also explains another question I had before, that the tick of the checkbox will be change after the check status is modified. I am curious though, what's the reason to create another widget except simply modify the "text property" of widget? Is the property somehow locked or encrypted by acrobat?

As a temporary solution, is it possible to get the parameters of the widget, and then generate a textbox to replace the filled information, so that it can support any font. But it is necessary to ensure that the widget can obtain all the required information, such as font / font size / line spacing, etc.

[JorjMcKie]

As a temporary solution, is it possible to get the parameters of the widget, and then generate a textbox to replace the filled information, so that it can support any font. But it is necessary to ensure that the widget can obtain all the required information, such as font / font size / line spacing, etc.

No, this is not possible. Every PDF software has its own way of setting up display details and font support. Like pages and annotations, widgets have their own "contents stream" (which is a little program written in a PDF-specific mini-language) responsible for all aspects of appearance.
That source program is highly software product specific.
There is no part of the PDF specification that limits a wide range of possibilities.