您可以尝试在PyQt中加载自定义CSS样式表，并将此CSS文件应用于HTML内容，从而在元素上产生所需的填充效果。

from PyQt5 import QtCore, QtWidgets, QtWebEngineWidgets

def printhtmltopdf(html_in, pdf_filename):
    app = QtWidgets.QApplication([])
    page = QtWebEngineWidgets.QWebEnginePage()

    def handle_pdfPrintingFinished(*args):
        print("finished: ", args)
        app.quit()

    def handle_loadFinished(finished):
        page.printToPdf(pdf_filename)

# added function
    def add_border_spacing():
        # Load a custom CSS style sheet with border spacing
        with open("style.css", "r") as file:
            css_content = file.read()
        page.setHtml(html_in, QtCore.QUrl().fromLocalFile(QtCore.QFileInfo("style.css").absoluteFilePath()))
        page.profile().scripts().insert(QtWebEngineWidgets.QWebEngineScript.DocumentCreation, css_content)

    page.pdfPrintingFinished.connect(handle_pdfPrintingFinished)
    page.loadFinished.connect(handle_loadFinished)

    page.setZoomFactor(1)

    add_border_spacing() # apply function

    app.exec()

printhtmltopdf(
    result, 
    "file.pdf",
)

样式CSS文件

border-spacing: 10px;
    padding: 20px;

style.css文件与Python脚本位于同一目录中。
也检查this答案。它使用javascript加载css。