What is "pdftk"

PDFtk (short for PDF Toolkit) is a cross-platform tool for manipulating Portable Document Format (PDF) documents. It comes in two versions: PDFtk Free ( open source) and PDFtk Pro ( proprietary paid). Many functions are not available in the open source version, but only in the paid proprietary one.

PDFtk is a front end to the iText library (compiled to native code using GCJ), capable of splitting, merging, encrypting, decrypting, uncompressing, recompressing, and repairing PDFs. It can also be used to manipulate watermarks, metadata, and to fill PDF Forms with FDF Data (Forms Data Format) or XFDF Data (XML Form Data Format).