Editing properties of a field

[ReedGraff]

Explanation

I'd love to be able to change field properties. Specifically, in Adobe, it is possible to change the background color of a signature field to yellow, red, or another color for example. If someone could point me in the right direction I would happily make this myself.

Code Example

I assume this could be done two ways, by extending or appending functionality to the update_ function, or by creating a new function in its entirety. The latter of which is probably easier.

from pypdf import PdfReader, PdfWriter

reader = PdfReader("SOMEPATH")
writer = PdfWriter()
writer.append(reader)

for page in range(len(reader.pages)):
    writer.update_page_form_field_properties(
    writer.pages[page],
    {
          'field1': {"background": "#ffffff", "font": "Helvetica"}, 
          'field2': {"fontSize": "14pt", "color": "#000000"},
    }
)

[pubpub-zz]

@ReedGraff
you can change font size and color adjusting /DA field before filling up (using PDF or any viewers) before. a method to change it has been drafted in #2064. Color could be introduced too
Changing font was also planned there however this is more tricky and is currently blocking the PR I've started.
for background color I have no find a way to do that.

Do you have any example of such documents ?

[ReedGraff]

Here's a demo in Adobe illustrating what I'd like to be able to do in pypdf.

Here's the example PDF.
HighlightingDemo.pdf

[stefan6419846]

Looking at the provided PDF file (in this case the uncompressed content stream version from pdftk, but should be similar in pypdf itself), we have (original xobj is 6):

113 0 obj

<<
/TU (Contact:)
/P 7 0 R
/Subtype /Widget
/T (Contact)
/F 4
/Type /Annot
/DA (/Helv  0 Tf 0 g)
/DR 
<<
/Font 
<<
/Helv 134 0 R
>>
/Encoding 
<<
/PDFDocEncoding 135 0 R
>>
>>
/FT /Tx
/MK 
<<
/BG [0.988235 0.956863 0.521576]
>>
/AP 
<<
/N 86 0 R
>>
/Rect [363.96 678.24 568.68 695.04]
>>
endobj

The most important difference to a regular field is

/MK 
<<
/BG [0.988235 0.956863 0.521576]
>>

in this case: /MK defines the "appearance characteristics dictionary" of the annotation (see table 188 of the PDF 1.7 specification) and the corresponding /BG key of this dictionary the "colour of the widget" (see table 189 of the PDF 1.7 specification).

For comparison: This is how the not highlighted phone field is defined (the original xobj is 12):

114 0 obj

<<
/TU (Phone:)
/P 7 0 R
/Subtype /Widget
/T (Phone)
/F 4
/Type /Annot
/DA (/Helv  0 Tf 0 g)
/DR 
<<
/Font 
<<
/Helv 134 0 R
>>
/Encoding 
<<
/PDFDocEncoding 135 0 R
>>
>>
/FT /Tx
/AP 
<<
/N 87 0 R
>>
/Rect [358.08 660 568.68 676.8]
>>
endobj

[ReedGraff]

Interesting, so how might I be able to create a function for this on top of the existing library?