Set XMP Metadata

This guide will show how to set an XMP pdf metadata.

Before you begin #

First of all you should get your API key from your UniCloud account.

If this is your first time using UniPDF SDK, follow this guide to set up a local development environment.

Project setup #

Clone the project repository #

In your terminal, clone examples repository. It contains the Go code we will be using for this guide.

git clone https://github.com/unidoc/unipdf-examples.git

Navigate to the metadata folder in the unipdf-examples directory.

cd unipdf-examples/metadata

Configure environment variables #

Replace the UNIDOC_LICENSE_API_KEY with your API credentials from your UniCloud account.

Linux/Mac #

export UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

Windows #

set UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

How it works #

The import section in lines 3-13 imports some unipdf packages and other necessary libraries. The init function in lines 21-28 loads your metered license key and authenticates your request.

In lines 30-144 the main function is defined. In this function in lines 31-37 the input and output files are read from the command line arguments. The code line 40-44 measures the time taken to process the document. In lines 47-57 a new pdfReader is instantiated and converted to pdfWriter object.

In lines 60-72 an XMP document is extracted from the document. If it doesn’t exist in the document a new one is created in lines 72-74. In lines 77-80 the PdfInfo in the original file is read using reader.GetPdfInfo(). The code in lines 83-93 sets the creationDate info of the document. The modifiedAt info is set in lines 95-101.

In lines 104-112 the PdfInfoOptions is created by setting pdfInfo, pdfVersion, copyright information fields. The pdfInfo is set using xmpDoc.SetPdfInfo(xmpPdfMetadata) in lines 114-117. Then the XMP document is marshaled into byte stream using xmpDoc.MarshalIndent("", "\t"). In line 129-132 a core.PdfObjectStream object is created from the byte stream using core.MakeStream(metadataBytes, nil).

In line 135-137 the metadata is set to the document using pdfWriter.SetCatalogMetadata. Finally the document is written to file using pdfWriter.WriteToFile(outputPath) in lines 140-143.

Run the code #

go run pdf_set_xmp_pdf_metadata.go <input.pdf> <output.pdf>