PDF 闲谈

 async function loadDocument(recoveryMode) {
    await pdfManager.ensureDoc("checkHeader");
    await pdfManager.ensureDoc("parseStartXRef");
    await pdfManager.ensureDoc("parse", [recoveryMode]);

    if (!recoveryMode) {
    // Check that at least the first page can be successfully loaded,
    // since otherwise the XRef table is definitely not valid.
        await pdfManager.ensureDoc("checkFirstPage");
    }

    const [numPages, fingerprint] = await Promise.all([
        pdfManager.ensureDoc("numPages"),
        pdfManager.ensureDoc("fingerprint"),
    ]);
    return { numPages, fingerprint };
}