As requested, here are direct download links to various documentation files:

IMSL C Numerical Library Version 7.0
Functionality
IMSL C Numerical Library Function Catalog (0.2MB PDF)

Documentation
IMSL C Numerical Library User's Guide, Volume 1 of 2: Math Library (5.5MB PDF)
IMSL C Numerical Library User's Guide, Volume 2 of 2: Stat Library (6.5MB PDF)
IMSL C Numerical Library User's Guide, Volume 1 of 2: Math Library (HTML)
IMSL C Numerical Library User's Guide, Volume 2 of 2: Stat Library (HTML)

IMSL C# Numerical Library for .NET Applications Version 6.5
Functionality
IMSL C# Library 6.5 Function Catalog (270 KB PDF)

Documentation
IMSL C# Library 6.5 API Description (HTML)
IMSL C# Library 6.5 Chart Programmers Guide (HTML)
IMSL C# Library 6.5 User's Guide (7.4MB PDF)
IMSL C# Library 6.5 Chart Programmers Guide (2.7MB PDF)

JMSL Numerical Library for Java Applications Version 6.1
Functionality
JMSL Library 6.1 Function Catalog (700KB PDF)

Documentation
JMSL Library 6.1 API Description (HTML)
JMSL Library 6.1 Chart Programmers Guide (HTML)
JMSL Library 6.1 Reference Manual (7.1MB PDF)
JMSL Library 6.1 Chart Programmers Guide (3.6MB PDF)

IMSL Fortran Numerical Library Version 7.0
Functionality
Fortran Library 7.0 Function Catalog (2MB PDF)

Documentation
IMSL Fortran Library User's Guide Math/Library (13.7MB PDF)
IMSL Fortran Library User's Guide Math/Library Special Functions (4MB PDF)
IMSL Fortran Library User's Guide Stat/Library (12.1MB PDF)
IMSL Fortran Library User's Guide Math/Library (HTML)
IMSL Fortran Library User's Guide Math/Library Special Functions (HTML)
IMSL Fortran Library User's Guide Stat/Library (HTML)

PyIMSL Version 1.6
Documentation
PyIMSL User's Guide, Volume 1 of 2: Math Library (6.8MB PDF)
PyIMSL User's Guide, Volume 2 of 2: Stat Library (4.3MB PDF)
PyIMSL User's Guide, Volume 1 of 2: Math Library (HTML)
PyIMSL User's Guide, Volume 2 of 2: Stat Library (HTML)

Getting Started
PyIMSL Studio on Linux/Windows - Getting Started (750KB PDF)