TCLFPDF is a port and, as such, is considered a derivative work, so its license is determined by the license of the original work from which it is derived.
TCLFPDF was originally a port of FPDF, a PHP library (by Olivier Plathey) that generates PDFs without any external dependencies.
However, tFPDF (by Ian Back and Tycho Veltmeijer) was later used as the reference source. This is a class derived from FPDF and includes UTF8 support, which FPDF lacks.
Speaking more specifically about licenses, we should mention that although, as stated on the FPDF home page: "F from FPDF stands for Free: you may use it for any kind of usage and modify it to suit your needs", to be precise, the FPDF license is not explicitly stated on its website or in its code, so according to the "license.txt" file distributed with the code, it could be interpreted as MIT or similar (see Appendix [1]).
On the other hand, tFPDF is distributed under the LGPL license.(see Appendix [2] )
Summarizing FPDF (MIT) -> tFPDF (LGPL) and so...
TCLFPDF is licensed under the GNU Lesser General Public License (LGPL).