Uploading Pdf file and images at the same time

Hi, there I’m working on a project and wanted to know how can I upload pdf file and images to rest api as I tried with filetransfer plugin but was unable to send. Then I was suggested to send in the form of formdata.
Can anybody help me with that.

below is my code…

this.pdfObj = pdfMake.createPdf(docDefinition);
      this.pdfObj.getBuffer((buffer) => {
        var blob = new Blob([buffer], { type: 'application/pdf' });

        // Save the PDF to the data Directory of our App
        this.file.writeFile(this.file.dataDirectory, 'myletter.pdf', blob, { replace: true })
          // Open the PDf with the correct OS tools
          // this.fileOpener.open(this.file.dataDirectory + 'myletter.pdf', 'application/pdf');
          // console.log("pdf");
            console.log("got till here") 
            //Show loading
            this.loading = this.loadingCtrl.create({
              content: "Uploading..."
            const fileTransfer: FileTransferObject = this.transfer.create();

            //option transfer
            let options: FileUploadOptions = {
              fileName: this.myletter,
              chunkedMode: false,
              httpMethod: 'post',
               params : {'i13': this.myletter}
            //file transfer action
            fileTransfer.upload(this.myletter, 'myapi.php', options)
              .then((data) => {
              console.log('Image succesful uploaded.');
                }, (err) => {
                console.log('Error while uploading file.');