How to fill checkbox in pdfium

[Muppalla Mounika]

I am trying to enable check using pdfium.

Below is my code to enable checkbox in pdfium acroform.

 int pageCount = FPDF_GetPageCount(doc);
    for (int i = 0; i < pageCount; ++i) {
        FPDF_PAGE page = FPDF_LoadPage(doc, i);
        FORM_OnAfterLoadPage(page, form); // Must call after loading the page
        FORM_DoPageAAction(page, form,FPDFPAGE_AACTION_OPEN); // Trigger any page actions

        int annotCount = FPDFPage_GetAnnotCount(page);
        for (int j = 0; j < annotCount; ++j) {
            FPDF_ANNOTATION annot = FPDFPage_GetAnnot(page, j);
            if (FPDFAnnot_GetSubtype(annot) == FPDF_ANNOT_WIDGET) {
                int fieldType = FPDFAnnot_GetFormFieldType(form, annot);
                if (fieldType == FPDF_FORMFIELD_CHECKBOX) {
                    FPDFAnnot_SetStringValue(annot, "V", GetFPDFWideString("Yes"));
                    FPDFAnnot_SetAP(annot, FPDF_ANNOT_APPEARANCEMODE_NORMAL, nullptr);
                }
            }

            FPDFPage_CloseAnnot(annot);
        }
        FORM_OnBeforeClosePage(page, form);
        FPDF_ClosePage(page);
    }

On editing PDF & checking details, I see the dictionary value is expected in format. How to achieve it? Also How to set appearance stream along with set value? 

/V /Off

 /V /Yes

[Justin Pierce]

You will have better luck with `FORM_OnLButtonDown` to emulate a click

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From: pdf...@googlegroups.com <pdf...@googlegroups.com> on behalf of Muppalla Mounika <muppall...@gmail.com>
Sent: Friday, November 1, 2024 8:41:21 PM
To: pdfium <pdf...@googlegroups.com>
Subject: How to fill checkbox in pdfium

 

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[Saveliy Vasilev]

It seems that it's not possible with the current public pdfium interface.

According to the manual (pp. 615, https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf); the way to check/uncheck a checkbox is to set /AS value (in annot dict) to match the dict entry in /AP -> /N; which in turn defines how a checked / unchecked box looks like. Apparently, the /Off value is the default for an unselected checkbox option (in /AP -> /N). Yet, there is no standard on how the checked dict entry should be called: I've seen different names within the same form multiple times. This means that the way to set the checkbox implies the following steps:

- Get the /Off and /<something else> options from the /AP -> /N dict from the annot

- Set the /AS to match <something else>

In fact, this is exactly what is done by the C++ code, `CPDFSDK_Widget::SetCheck(bool bChecked)` is a function (not public) that given a checkbox / radio button widget sets the value to `bChecked`. Indeed, the function calls the following that does the job:

void CPDF_FormControl::CheckControl(bool bChecked) {
  DCHECK(GetType() == CPDF_FormField::kCheckBox ||
         GetType() == CPDF_FormField::kRadioButton);
  ByteString csOldAS = m_pWidgetDict->GetByteStringFor("AS", "Off");
  ByteString csAS = "Off";
  if (bChecked)
    csAS = GetOnStateName();
  if (csOldAS == csAS)
    return;
  m_pWidgetDict->SetNewFor<CPDF_Name>("AS", csAS);
}

All this being said, we don't have any exported function that would set the CPDF_Name for a dict. We can only set CPDF_String values, which wraps the string in parenthesis which signals the PDF that it should be treated as a string and not as dict value.

If time allows, I might open a CL to pdfium so we can have some function as FPDFAnnot_SetChecked function for this case. I managed to get it working but I'm missing the tests and it would require compiling pdfium and not relying on the official binaries.

All the best!

[Justin Pierce]

It is possible, albeit a bit cumbersome. You can use the form filler API to toggle the value of a checkbox:

FPDFAnnot_GetRect();

FORM_OnLButtonDown();

FORM_OnLButtonUp();

Get Outlook for Android

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From: pdf...@googlegroups.com <pdf...@googlegroups.com> on behalf of Saveliy Vasilev <sav...@tukki.ai>
Sent: Wednesday, March 19, 2025 2:43:29 AM
To: pdfium <pdf...@googlegroups.com>
Subject: Re: How to fill checkbox in pdfium

 

To view this discussion visit https://groups.google.com/d/msgid/pdfium/8f7b8a5d-f8f1-4835-bbe4-a0e5b8d64741n%40googlegroups.com.