Attach (recommended) or Link to PDF file here:
[Testfile v1.5 to PDFA2.pdf](https://github.com/mozilla/pdf.js/files/6310752/Testfile.v1.5.to.PDFA2.pdf)


Configuration:
- Web browser and its version: Version 89.0.4389.114 (Offizieller Build) (x86_64)
- Operating system and its version: Windows 10 / MacOS BigSur
- PDF.js version: 2.5.207
- Is a browser extension: no 

Steps to reproduce the problem:
1.  Open Testfile v1.5 to PDFA2.pdf in pdf.js viewer demo
2. text is covered up by markings / highlights which are stored in pdf itself

What is the expected behavior? (add screenshot)
Should be displayed as in Acrobat Reader
<img width="1169" alt="Bildschirmfoto 2021-04-14 um 14 24 41" src="https://user-images.githubusercontent.com/1286150/114710202-bf175a80-9d2d-11eb-8d54-75481fe91b7d.png">

What went wrong? (add screenshot)
It's how it is displayed in pdf.js viewer
<img width="782" alt="Bildschirmfoto 2021-04-14 um 14 24 16" src="https://user-images.githubusercontent.com/1286150/114710311-d8200b80-9d2d-11eb-8000-b67b94488929.png">

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

);
    }
    if (alignment === 0 || alignment > 2) {
      
      return (
        "/Tx BMC q BT " +
        defaultAppearance +
        ` 1 0 0 1 ${hPadding} ${vPadding} Tm (${escapeString(
          encodedString
        )}) Tj` +
        " ET Q EMC"
      );
    }
    const renderedText = this._renderText(
      encodedString,
      font,
      fontSize,
      totalWidth,
      alignment,
      hPadding,
      vPadding
    );
    return (
      "/Tx BMC q BT " +
      defaultAppearance +
      ` 1 0 0 1 0 0 Tm ${renderedText}` +
      " ET Q EMC"
    );
  }
  async _getFontData(evaluator, task) {