According to the XFDF specification:
XFDF (XML Forms Data Format) is a format for representing forms data and annotations in a PDF document. XFDF is the XML version of Forms Data Format (FDF), a simplified version of PDF for representing forms data and annotations.
Examples
<?xml version="1.0" encoding="UTF-8" ?>
<xfdf xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve">
<fields>
<field name="ACombo"><value>Red</value></field>
</fields>
<annots>
<square subject="Rectangle" page="0" rect="306.01,744.85,408.98,775.94" flags="print" name="447c49b7-5e50-4b13-adc8-c291102466e6" title="Guest" date="D:20171226120150-08'00'" color="#000000" width="5" creationdate="D:20171226120147-08'00'">
<popup flags="print,nozoom,norotate" page="0" rect="0,767,112.5,842" open="no"/>
</square>
</annots>
</xfdf>
The fields section contains the names and values of any form fields in the document. In annots all of the annotation data is found.
In PDF.js Express Web Viewer
PDF.js Express provides methods to import annotations into the viewer from their XFDF data as well as export all currently loaded annotations as XFDF using AnnotationManager.
WebViewer(...)
.then(instance => {
const { annotManager } = instance;
// import asynchronously
// you might call this after fetching the XFDF data as a string from your server
annotManager.importAnnotations(xfdfData).then(importedAnnotations => { });
// get all annotation and form data
// you might call this when you want to pass the XFDF data to your server to be saved
// or you may want to pass an XFDF string to doc.getFileData to embed the annotations
// in the downloaded PDF
annotManager.exportAnnotations().then(xfdfData => { });
// if you're saving the XFDF to your server and calling importAnnotations when loading
// you may not want to save the widgets and links if they won't be changing in the document
// this is because widgets and links don't have unique ids so WebViewer isn't always able
// to merge them together without duplicating them when calling importAnnotations
// as long as you save the field values then changes made to the fields (e.g. checking a checkbox)
// will be saved
// if you don't need to save field values either you can use "fields: false"
annotManager.exportAnnotations({
widgets: false,
links: false
//fields: false
}).then(annotData => { })
// only get XFDF data for specified annotations
// this might be useful if you save the XFDF data separately per user on your server
// and you want to get the XFDF data for a particular user's annotations
// it can also be useful if you want to get the XFDF for a particular annotation
// because you're saving each annotation in a separate database row on your server
annotManager.exportAnnotations({
annotList: [annot1, annot2]
}).then(annotData => { })
})
WebViewer(...)
.then(instance => {
const { annotationManager } = instance.Core;
// import asynchronously
// you might call this after fetching the XFDF data as a string from your server
annotationManager.importAnnotations(xfdfData).then(importedAnnotations => { });
// get all annotation and form data
// you might call this when you want to pass the XFDF data to your server to be saved
// or you may want to pass an XFDF string to doc.getFileData to embed the annotations
// in the downloaded PDF
annotationManager.exportAnnotations().then(xfdfData => { });
// if you're saving the XFDF to your server and calling importAnnotations when loading
// you may not want to save the widgets and links if they won't be changing in the document
// this is because widgets and links don't have unique ids so WebViewer isn't always able
// to merge them together without duplicating them when calling importAnnotations
// as long as you save the field values then changes made to the fields (e.g. checking a checkbox)
// will be saved
// if you don't need to save field values either you can use "fields: false"
annotationManager.exportAnnotations({
widgets: false,
links: false
//fields: false
}).then(annotData => { })
// only get XFDF data for specified annotations
// this might be useful if you save the XFDF data separately per user on your server
// and you want to get the XFDF data for a particular user's annotations
// it can also be useful if you want to get the XFDF for a particular annotation
// because you're saving each annotation in a separate database row on your server
annotationManager.exportAnnotations({
annotList: [annot1, annot2]
}).then(annotData => { })
})
PDF.js Express also provides a way to get the XFDF data for annotations that have changed recently in the viewer. AnnotationManager.exportAnnotCommand will get the XFDF data for annotations that have been added, modified or deleted since the last time exportAnnotCommand was called.
A command looks something like this:
<?xml version="1.0" encoding="UTF-8" ?>
<xfdf xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve">
<fields />
<add>
<text subject="Comment" page="0" rect="262.13,465.90,285.38,489.15" flags="print,nozoom,norotate" name="651eab92-9258-f676-b5c0-9767cb1ab932" title="Guest" date="D:20171226125004-08'00'" color="#FFFF00" opacity="0.5" creationdate="D:20171226125004-08'00'" icon="Comment">
<popup flags="print,nozoom,norotate" page="0" rect="0,573,112.5,648" open="no"/>
</text>
</add>
<modify>
<text subject="Comment" page="0" rect="110.47,367.84,133.72,391.09" flags="print,nozoom,norotate" name="e89d6405-fdcc-aa2b-9ebb-cc9d8a525ca2" title="Guest" date="D:20171226125247-08'00'" color="#FFFF00" opacity="0.5" creationdate="D:20171226125238-08'00'" icon="Comment">
<popup flags="print,nozoom,norotate" page="0" rect="0,573,112.5,648" open="no"/>
</text>
</modify>
<delete>
<id page="0">e2976b7b-075b-cad9-0f9f-fe0de613a543</id>
</delete>
</xfdf>
Commands can be imported using AnnotationManager.importAnnotCommand. This is the technique that is used in the realtime collaboration example.
To merge annotations directly into the document PDF.js Express offers a REST API. This can also be used when importing pre-existing annotation made within a PDF.
