I understand you're looking for the in PDF format, likely free of charge.
gfortran (supports -std=legacy) or f77 via gcc on Linux.MinGW or DOSBox with Microsoft Fortran PowerStation (abandonware but legal to download)."Schaum's Outline of Programming with FORTRAN 77" by Mayo and Cwiakala provides a comprehensive guide to FORTRAN 77, covering core logic, data handling, and control structures. A digital copy of this 1995 text is available for borrowing through the Internet Archive. For free access to the text, visit Internet Archive . Schaum's Outline of Programming with Fortran 77 I
You can often "borrow" a digital copy of this book for free through their library system. "Schaum's Outline of Programming with FORTRAN 77" by
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offers a professional breakdown of variables, declarations, and common syntax errors. University of Texas at Austin Tutorial covering core logic
: Much of the world's most critical infrastructure for weather forecasting and structural engineering still runs on refined Fortran 77 code.