Error: "This PDF document probably uses a compression technique which is not supported by the free parser shipped with FPDI."
By default FPDI can "only" handle PDF documents with a normal cross-reference which was the default way to store object offsets in a PDF document up to PDF version 1.4. Beginning with PDF version 1.5 there were new compression features introduced which involve internal structure changes how a PDF document can be created.
We offer a commercial addon which enables FPDI to handle documents that uses these compression features.
Alternatively the document you're trying to import has to be resaved without the use of compressed cross-reference streams and objects by an external programm (e.g. by lowering the PDF version to 1.4).