Attach (recommended) or Link to PDF file here:
[docOficialPDF.php.pdf](https://github.com/mozilla/pdf.js/files/7159923/docOficialPDF.php.pdf)

Configuration:
- Web browser and its version: Firefox nightly
- Operating system and its version: linux debian
- PDF.js version: built-in viewer
- Is a browser extension: no

Steps to reproduce the problem:
1. Open the pdf page 2
2. Checkbox "Alta" in section 2 must be checked

It works fine with evince.
const customAppearance = params.dict.get("AP");
    if (!isDict(customAppearance)) {
      return;
    }
    const normalAppearance = customAppearance.get("N");
    if (!isDict(normalAppearance)) {
      return;
    }
    
    
    const asValue = this._decodeFormValue(params.dict.get("AS"));
    if (typeof asValue === "string") {
      this.data.fieldValue = asValue;
    }
    const exportValues = normalAppearance.getKeys();
    if (!exportValues.includes("Off")) {
      
      exportValues.push("Off");
    }
    
    
    if (!exportValues.includes(this.data.fieldValue)) {
      this.data.fieldValue = null;
    }
    if (exportValues.length !== 2) {
      return;
    }
    this.data.exportValue =
      exportValues[0] === "Off" ? exportValues[1] : exportValues[0];