Ghostscript

Ghostscript is an interpreter for the PostScript language and PDF files, and one of those quiet pieces of software that ends up inside far more products than most people realize. If you have ever converted a PostScript document to PDF, printed through CUPS on a Unix system, or used a PDF tool that needed to rasterize pages, there is a good chance Ghostscript was doing the work underneath.

The core job is simple to state: take PostScript or PDF input and turn it into something else. That output can be pages rendered on screen, raster images in formats like PNG, JPEG or TIFF, print-ready data for a huge range of printer drivers, or a fresh PDF that has been optimized, downsampled or repaired. Everything runs from the command line or through a library API, which is why Ghostscript shows up as the engine inside print servers, document pipelines, LaTeX toolchains and plenty of commercial products.

For day-to-day use, most people touch Ghostscript through a frontend rather than directly. Viewers like GSview put a window around it, and tools such as ImageMagick, Scribus and CUPS call it behind the scenes. If you are comfortable in a terminal, though, Ghostscript itself is remarkably capable: a single invocation can compress a bloated PDF, extract specific pages, convert a document to images at a chosen resolution, or merge several files into one. Scripts and scheduled jobs can lean on it for bulk processing that would take hours by hand.

The project is maintained by Artifex Software and ships under a dual license. The AGPL release is free for open-source and personal use, while a commercial license covers proprietary products that embed the interpreter. Releases arrive regularly, tracking PDF specification updates and shipping security fixes, which matters for a component that parses untrusted documents from the outside world. Official downloads for Windows, Linux and macOS are published on the project's GitHub releases page, including 64-bit Windows installers and source archives.

Ghostscript is not the friendliest tool you will ever install. The option list runs into the hundreds, the documentation assumes some familiarity with page description languages, and error messages can be terse. It also does exactly what you ask, with no preview and no undo, so first attempts at PDF compression settings often take a couple of tries. Still, for its niche - precise, scriptable PostScript and PDF processing - it remains the reference implementation that other tools are measured against, and it costs nothing to use.