丹尼尔的回答很有帮助。但有两行需要更正：

let centerText = setTextCenter(pages[0], font, fontSize)

let rightText = setTextRight(pages[0], font, fontSize)

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你可以这样使用widthOfTextAtSize字体属性：

const pdfDoc = await PDFDocument.load(file) 
const pages = pdfDoc.getPages()
const font = await pdfDoc.embedFont(StandardFonts.TimesRoman)
const fontSize = 10

let centerText = setPageTextCenter(pages[0], font, fontSize)

centerText('This text is center aligned', xPos, yPos)

let rightText = setPageTextCenter(pages[0], font, fontSize)

rightText('this text is right aligned', xPos, yPos)

const setTextCenter = (page, font, size) => {
    return (text, x, y) => {
        const widthText = font.widthOfTextAtSize(text, size)
        const props = {
            x: x - widthText / 2,
            y: y,
            size,
            font,
       }
       page.drawText(text, props)
    }
}

const setTextRight = (page, font, size) => {
    return (text, x, y) => {
        const widthText = font.widthOfTextAtSize(text, size)
        const props = {
            x: x - widthText,
            y: y,
            size,
            font,
       }
       page.drawText(text, props)
    }
}

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