Edit PDF metadata on Android

Metadata may be stored in a PDF document in two ways: in a document information dictionary associated with the document, or in a metadata stream containing XMP data. To give you full access to all the PDF metadata, Nutrient comes with DocumentPdfMetadata and DocumentXmpMetadata, which allow you to retrieve or modify a document’s metadata.

PDF metadata

Use DocumentPdfMetadata to work with the dictionary-based metadata in a PDF.

All values specified in the PdfValue are represented by the following types:

• Boolean

• long

• double

• String

• List<PdfValue>

• Map<String, PdfValue>

By default, the dictionary metadata may contain the following information keys:

• Author

• CreationDate

• Creator

• Keywords

• ModDate

• Producer

• Title

You can, of course, add any supported key-value dictionary to the metadata. When dealing with these predefined keys, it’s recommended to use the DocumentPdfMetadata getters and setters so that you get out-of-the-box conversions from objects such as Date.

Retrieving PDF metadata

To get an entry of the metadata dictionary (e.g. the Author), you can use the following code snippet:

val document = ...
val pdfMetadata = document.getPdfMetadata()
val author = pdfMetada.getAuthor()

PdfDocument document = ...
DocumentPdfMetadata pdfMetadata = document.getPdfMetadata();
String author = pdfMetadata.getAuthor();

For any custom values, use this:

val document = ...
val pdfMetadata = document.pdfMetadata
val value = pdfMetada.get("Custom key")

PdfDocument document = ...
DocumentPdfMetadata pdfMetadata = document.getPdfMetadata();
PdfValue value = pdfMetadata.get("Custom key");

Saving PDF metadata

You can customize the document metadata and then save the document, which also saves the modified metadata into the PDF:

val pdfMetadata = document.pdfMetadata
val metadataKey = "Key"
pdfMetadata.set(metadataKey, PdfValue(3))
document.saveIfModified()

DocumentPdfMetadata pdfMetadata = document.getPdfMetadata();
String metadataKey = "Key";
pdfMetadata.set(metadataKey, new PdfValue(3));
document.saveIfModified();

XMP metadata

Use DocumentXmpMetadata to work with the metadata stream containing XMP data.

Each key in the XMP metadata stream has to have a namespace set. You can define your own namespace or use one of the already existing ones. PSPDFKit exposes two constants for common namespaces:

• DocumentPdfMetadata#XMP_PDF_NAMESPACE/DocumentPdfMetadata#XMP_PDF_NAMESPACE_PREFIX — the XMP PDF namespace created by Adobe §3.1

• DocumentXmpMetadata#XMP_DC_NAMESPACE/DocumentXmpMetadata#XMP_DC_NAMESPACE_PREFIX — the Dublin Core namespace

When setting a value, you also have to pass along a suggested namespace prefix, as this can’t be generated automatically.

Retrieving XMP metadata

Use the following code snippet to get an object from the XMP metadata:

val xmpMetadata = document.xmpMetadata
val pdfValue = xmpMetadata.get("Key", NAMESPACE)

DocumentXmpMetadata xmpMetadata = document.getXmpMetadata();
PdfValue pdfValue = xmpMetadata.get("Key", NAMESPACE);

Saving XMP metadata

You can also set new metadata and save it to the document:

val xmpMetadata = document.xmpMetadata

val metadataKey = "MyKey"
val metadataValue = "MyValue"

xmpMetadata.set(metadataKey, metadataValue, NAMESPACE, NAMESPACE_PREFIX)

DocumentXmpMetadata xmpMetadata = document.getXmpMetadata();

String metadataKey = "MyKey";
String metadataValue = "MyValue";

xmpMetadata.set(metadataKey, metadataValue, NAMESPACE, NAMESPACE_PREFIX);