Processing PDFs

In this next section, we will address all the input and output operations that allow the user to properly handle PDF files.

Environment

• Supported on Desktop.

Including the PDF addon

To include the PDF addon, simply add a reference to the corresponding JavaScript file, included in the resources folder.

<script src="Resources/addon/dynamsoft.webtwain.addon.pdf.js"></script>

If you are using the dwt package, the pdf addon is already included in the main JavaScript file ( dynamsoft.webtwain.min.js or dynamsoft.webtwain.min.mjs ) which means you can skip this step.

Input

Open an image-only PDF file

If the PDF file only has one image per page, it can load the file by extracting the images. Most of the PDF files are scanned documents.

Open a PDF file with more than images

If the PDF file is not pure image, we need to make use of the PDF Rasterizer (PDFR for short) to render the PDF first.

How PDFR works: As the name suggests, PDFR rasterizes a PDF file page by page much like a scanner. You set a resolution, and you get the resulting images in that resolution after the rasterization.

The following code shows the basic usage

var onSuccess = function() {
    console.log("Loaded a file successfully!");
};
var onFailure = function(errorCode, errorString) {
    console.log(errorString);
};
DWTObject.IfShowFileDialog = true;
// PDF Addon is used here to ensure text-based PDF support
DWTObject.Addon.PDF.SetReaderOptions({
    convertMode: Dynamsoft.DWT.EnumDWT_ConvertMode.CM_RENDERALL,
    renderOptions:{
        renderAnnotations: true;
    }
});
DWTObject.LoadImageEx("", Dynamsoft.DWT.EnumDWT_ImageType.IT_ALL, onSuccess, onFailure);

The method SetReaderOptions() configures how a PDF will be rasterized when being loaded into Dynamic Web TWAIN.

Other methods

• GetReaderOptions(): This method returns the current ReaderOptions.

Output as PDF

Save images as image-based PDFs

Dynamic Web TWAIN can output one or multiple images in the buffer as image-based PDF file(s). This feature is built into the core module, and no addon is required as was covered in the output section.

PDF save settings

However, some advanced features are only possible with the help of the PDF addon. At present, that means configuring the resulting file(s) with the API Write.Setup() as shown below

DWTObject.Addon.PDF.Write.Setup({
    author: "Dynamsoft-Support-Team",
    compression: Dynamsoft.DWT.EnumDWT_PDFCompressionType.PDF_JP2000,
    pageType:Dynamsoft.DWT.EnumPDF_Page_A4,
    creator: "DWT",
    creationDate: "D:20200930",
    keyWords: "TWAIN, DWT, Dynamsoft",
    modifiedDate: "D:20200930",
    producer: "Dynamsoft Corporation",
    subject: "Demoing File",
    title: "Sample PDF Made by DWT",
    version: 1.5,
    quality: 80
});
DWTObject.IfShowFileDialog = true;
DWTObject.SaveAllAsPDF(' ', function() {}, function() {})

From version 18.5, Dynamic Web TWAIN supports the generation of encrypted PDF files. For example,

DWTObject.Addon.PDF.Write.Setup({
    author: "Dynamsoft-Support-Team",
    compression: Dynamsoft.DWT.EnumDWT_PDFCompressionType.PDF_JP2000,
    pageType:Dynamsoft.DWT.EnumPDF_Page_A4,
    creator: "DWT",
    creationDate: "D:20200930",
    keyWords: "TWAIN, DWT, Dynamsoft",
    modifiedDate: "D:20200930",
    producer: "Dynamsoft Corporation",
    subject: "Demoing File",
    title: "Sample PDF Made by DWT",
    version: 1.5,
    quality: 80,
    password: "dwtpassword"
});
DWTObject.IfShowFileDialog = true;
DWTObject.SaveAllAsPDF(' ', function() {}, function() {})

When you set a password prior to generating a PDF file, that password becomes necessary each time you attempt to open the file thereafter. The password does not restrict the usage permissions of the PDF. The encryption algorithm utilized is AES256, ensuring robust security measures.

Note: Only the core module license is required to use this method.

Append Pages to a PDF

If you need to append a scanned document to a PDF file and keep the rest pages unmodified. You can use the following code to read a PDF file by setting the preserveUnmodifiedOnSave property to true.

DWTObject.Addon.PDF.SetReaderOptions({
  convertMode: Dynamsoft.DWT.EnumDWT_ConvertMode.CM_RENDERALL,
  preserveUnmodifiedOnSave: true, //only available for v19.0+
});

Then, it will keep the unmodified pages in the PDF file instead of converting them to images when saving a new PDF file with the scanned documents.

PDF/A

PDF/A is a version of PDF specialized for use in the archiving and long-term preservation of electronic documents. For example, it does not allow using external fonts, which will change the appearance if opening it on another device.

Starting from Web TWAIN v19.3, it can save PDF as PDF/A-1b or PDF/A-2b by specifying pdfaVersion in PDFWSettings.

Here is the code to do this:

DWTObject.Addon.PDF.Write.Setup({
    pdfaVersion:"pdf/a-1b"
});
DWTObject.IfShowFileDialog = true;
DWTObject.SaveAllAsPDF(' ', function() {}, function() {})

Both PDF/A-1b and PDF/A-2b are basic conformation level standards. PDF/A-1b is based on PDF version 1.4 and PDF/A-2b is based on PDF version 1.7. PDF/A-2b has the following new features compared to PDF/A-1b:

• JPEG 2000 image compression.
• support for transparency effects and layers.
• embedding of OpenType fonts.
• provisions for digital signatures in accordance with the PDF Advanced Electronic Signatures – PAdES standard.
• the option of embedding PDF/A files to facilitate archiving of sets of documents with a single file.

It is recommended to use PDF/A-2b because of the support for more features.

Related FAQ:

• How can I generate PDF/A files?
• How can I load PDF/A files into the Dynamic Web TWAIN SDK?