HPGL and PLT File Format – HPGL/2 Plotter Files Explained

HPGL, HPGL/2 and PLT files are widely used in CAD plotting, engineering documentation and technical drawing workflows. These formats were designed for plotters and technical printers, allowing precise vector-based output for drawings and schematics.

Typical file extensions: .plt, .hpgl, .hpg, .gl2
Format type: vector-based plotter and printer command format
Common use: CAD plotting, engineering drawings, architecture and technical documentation

What Is a PLT File?

A PLT file is commonly used as a plotter output file. In many CAD workflows, PLT files contain vector-based plotting instructions generated by technical drawing software.


The PLT extension itself does not define one single internal format, but many PLT files contain HPGL or HPGL/2 commands. These commands describe how a plotter or printer should draw lines, text, curves and technical graphics.

What Is HPGL?

HPGL stands for Hewlett-Packard Graphics Language. It was originally developed by Hewlett-Packard for controlling pen plotters.


HPGL files contain commands that instruct a plotter how to draw graphics. Typical commands define pen movement, pen selection, coordinates, line drawing and text output.


Because HPGL is vector-based and compact, it became widely used in CAD systems, engineering environments and technical plotting workflows.

What Is HPGL/2?

HPGL/2 is an enhanced version of HPGL. It introduced improvements such as better line width handling, color support and more efficient plotting instructions.


HPGL/2 became common in many large-format printers and plotters, especially for CAD and engineering applications where precise technical output was important.

Where Are HPGL and PLT Files Used?

HPGL and PLT files are still found in many engineering and technical documentation workflows, especially where older CAD systems or archived plot files are involved.

Common Use Cases

  • CAD plotting
  • Engineering drawings
  • Architectural drawings
  • Manufacturing documentation
  • Technical schematics
  • Large-format printing
  • Legacy plotter archives

Why These Formats Were Popular

  • Compact vector drawing instructions
  • Designed for technical plotting
  • High precision line graphics
  • Efficient plotting and printing
  • Widely supported by CAD systems

HPGL and PLT Compared with PDF and DXF

HPGL and PLT files are mainly output-oriented formats designed for plotting and printing technical drawings. Other technical formats serve different purposes:

For sharing and archiving, converting HPGL or PLT files to PDF or image formats is often the most practical solution.

View, Print and Convert HPGL and PLT Files with ViewCompanion Standard

ViewCompanion Standard can open HPGL, HPGL/2 and PLT files and convert them to formats such as PDF, TIFF, PNG and JPEG. This makes it easier to work with legacy plotter files without requiring the original CAD application or plotter driver.

Learn more about ViewCompanion Standard

What Can ViewCompanion Do with HPGL and PLT Files?

ViewCompanion is a viewer and converter for technical document and drawing formats, including HPGL, HPGL/2 and PLT plotter files.

View and Inspect Plotter Files

  • Open PLT files in Windows
  • Open HPGL and HPGL/2 files
  • Zoom and pan technical drawings
  • Inspect plotted CAD output
  • Print plotter drawings

Convert HPGL and PLT Files

  • Convert PLT to PDF
  • Convert HPGL to PDF
  • Convert PLT to TIFF
  • Convert PLT to PNG or JPEG
  • Batch convert multiple files

Useful for Legacy CAD and Plotter Workflows

Many organizations still maintain archives containing PLT, HPGL or HPGL/2 files generated by older CAD systems. ViewCompanion helps make these files easier to access, print and convert into modern formats such as PDF and TIFF.


Batch Conversion and Automation

ViewCompanion supports batch conversion of HPGL and PLT files, making it possible to process large numbers of technical drawings automatically. This can be useful for archive conversion, engineering document management and migration projects.

Benefits of Converting HPGL and PLT Files

HPGL and PLT File Format FAQ

What is a PLT file?

A PLT file is often a plotter file containing drawing instructions generated by CAD or technical drawing software.


What does HPGL stand for?

HPGL stands for Hewlett-Packard Graphics Language.


What is HPGL/2?

HPGL/2 is an improved version of HPGL with support for better plotting, line widths and more efficient data.


Are PLT and HPGL the same thing?

Not always. PLT is commonly used as a file extension, while HPGL and HPGL/2 are plotting languages.


Can ViewCompanion open HPGL and PLT files?

Yes. ViewCompanion can open HPGL, HPGL/2 and PLT files for viewing, printing and conversion.


Can HPGL files be converted to PDF?

Yes. ViewCompanion can convert HPGL and PLT files to PDF and other supported formats.


Can I batch convert HPGL or PLT files?

Yes. Batch conversion is supported for large collections of plotter files.

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