我试图访问驻留在wwwRoot中的两个文件夹。这些文件夹是“BlankPDFFiles”和“FilledPDFFiles”。我试图获取驻留在BlankPDFFiles文件夹中的空白PDF文件，并在文件中写入一些数据，然后将其保存到FilledPDFFiles文件夹中。这是我的解决方案的结构：

当我尝试访问空白PDF文件时，出现以下错误：

下面是我的代码

public class PDFController : Controller
    {
        private readonly IEmployeeService _employeeService;
        public readonly IConfiguration _configuration;
        public readonly ILogger _logger;
        private readonly IWebHostEnvironment _environment;
        public PDFController(IEmployeeService employeeService, IConfiguration configuration, ILogger<PDFController> logger, IWebHostEnvironment environment)
        {
            _employeeService = employeeService;
            _configuration = configuration;
            _logger = logger;
            _environment = environment;
        }

        public async Task<IActionResult> Index()
        {
          
            await PopulatePDFDoc();
            return View();
        }

  public  async Task PopulatePDFDoc()
        {
            AckPackage.Data.PDFPopulate.DocPDF doc = new Data.PDFPopulate.DocPDF();
            string pdfLic = _configuration["PDFLicense"].ToString();
            string filledPDF = Path.Combine(_environment.WebRootPath, "FilledPDFFiles");
            string blankPDF = Path.Combine(_environment.WebRootPath, "BlankPDFFiles");
            EmployeeInfo employee =  await _employeeService.GetEmployeeByEmployeeNumber(up.EmployeeId);
            await doc.popolatePDFDoc(pdfLic, filledPDF, blankPDF, employee);

        }

这是我在populatePDFDoc方法中的内容：

public async Task  popolatePDFDoc(string PDFLic, string filledPDF, string blankPDF, EmployeeInfo employee)
        {
            
            string pathToFile = filledPDF + "_Package"+ "_" + employee.EmployeeNumber;
            bool validLicense = BitMiracle.Docotic.LicenseManager.HasValidLicense;
           
            **using (PdfDocument pdf = new PdfDocument(blankPDF))**
            {
                foreach (PdfControl control in pdf.GetControls())
                {
                    switch (control.Name)
                    {
                        case "EmpID":
                            ((PdfTextBox)control).Text = employee.EmployeeNumber;
                            break;
                        case "Last Name":
                            ((PdfTextBox)control).Text = employee.LastName;
                            break;
                    }
                }
                pdf.Save(pathToFile);
            }

我在popolatePDFDoc中的此行收到错误

using (PdfDocument pdf = new PdfDocument(blankPDF))

我正在使用第三方供应商工具来填充PDF文件。