What is the PLT file format?
Files with the .plt extension are most often created by AutoCAD and other CAD applications when you "plot to file." .plt is a vector-based plotter file that stores geometrical shapes, lines, arcs, and drawing objects as pen-plotter commands rather than as pixels.
.plt files are used by plotters to reproduce technical drawings using lines instead of dots, so artwork scales without any loss of quality. The format is based on the HP-GL/2 standard - a plain-text command language developed by Hewlett-Packard in which two-letter mnemonics such as IN, SP, PU, PD, and PA tell the plotter which pen to select and where to move it.
One important caveat: when AutoCAD plots to a .plt file, the content depends on the driver selected - it may be HP-GL/2, .PS, or PCL. Checking the opening bytes (IN; signals HP-GL/2) confirms the actual format. Related formats include .DXF, .DWG, and .SVG.
Security & safety
RISK: LOWHP-GL .plt files are plain text command streams and are not executable, so they pose little direct risk. The practical pitfalls are non-security: a .plt may not actually be HP-GL (it can be PostScript or PCL from a CAD print driver), so a viewer may show nothing - check the contents. Avoid sketchy "free PLT converter" download portals bundling adware/PUPs; prefer the reputable viewers above or browser-based converters, and don't upload confidential engineering drawings to unknown online services.
Format details
in a nutshellFULL NAMEHP-GL/2 Plotter File (HPGL)
DEVELOPERHewlett-Packard (HP-GL / HP-GL/2 language)since HP-GL late 1970s; HP-GL/2 1990s
CATEGORYVector Image Files
MIME TYPEapplication/vnd.hp-hpgl
TYPEPlain-text vector plotter command language (pen-plotter instructions)
STANDARDOpen · royalty-free
This extension is also used by…
- AutoCAD/CAD generic plot-to-file output - CAD apps emit .plt for any 'plot to file' driver, so a .plt may actually be PostScript or PCL data, not HP-GL.
- Vinyl/laser cutter cut files - Sign-cutting and laser software (e.g. ArtCut) use HP-GL .plt as the cutting-path language for plotters/cutters.
- Gerbv / other niche apps' plot files - Various scientific and mapping tools (Surfer, OziExplorer) export .plt route/contour data unrelated to HP-GL.
Programs that open PLT files
Windows4 apps
AutoCAD
Paid AutoCAD CREATES .plt via plot-to-file; to re-import a plot use a PLT/HPGL import tool - AutoCAD doesn't natively re-open arbitrary .plt as a drawing. 
Inkscape
Open-source Inkscape can OUTPUT HPGL for cutters and import some HPGL; open via File > Import. Good free route to SVG. 
ViewCompanion (Standard/Pro)
Paid Open the .plt to view HP-GL/HP-GL2/PCL/Calcomp plots and convert to PDF/TIFF/DXF/SVG. Free trial available.
Free PLT Viewer / Free HPGL Viewer
Free Open the .plt to view and resize HPGL/HPGL2 plots and export to BMP/JPG/PNG/TIFF. 
macOS1 app
ViewCompanion (via converters) / Inkscape
Open-source Use Inkscape (cross-platform) to import HPGL and export SVG/PDF; native Mac HPGL viewers are scarce. 
Linux1 app
Inkscape
Open-source Import HPGL .plt and export to SVG/PDF; also useful to generate HPGL for cutters.
Web1 app
Convertio (PLT converter)
Freemium Upload the .plt and convert to PDF, SVG, DXF, AI, JPG, EPS in the browser. Technical details
deep spec| Format type | Plain-text vector plotter command language (HP-GL/2) |
| Developed by | Hewlett-Packard - HP-GL introduced late 1970s; HP-GL/2 extended in the early 1990s |
| File structure | ASCII text stream of two-letter mnemonics (IN, SP, PU, PD, PA…) separated by semicolons |
| MIME type | application/vnd.hp-hpgl |
| File signature | No fixed binary magic bytes; files typically begin with IN; (Initialize) or ESC %-1B sequences for HP-GL/2 |
| Coordinate system | Plotter units (1/40 mm per unit in HP-GL/2); absolute positioning via PA or relative via PR |
| Pen model | SP (Select Pen) command switches pens; HP-GL supports up to 8 pens, HP-GL/2 up to 256 |
| Raster support | HP-GL/2 adds raster image transfer commands (RF); original HP-GL is vector-only |
| Character encoding | 7-bit ASCII; no binary, Unicode, or compressed content |
| Driver dependency | AutoCAD's .plt output content varies by plotter driver - may be HP-GL/2, PostScript, or PCL |
| Compression | None; raw ASCII command stream with no packaging or container layer |
| Page definition | Page size set by PS command and input-point pair (IP); supports ISO A-series and ANSI D/E formats |
| Common origin | Typically generated by CAD software (AutoCAD, BricsCAD, LibreCAD) via a plot-to-file workflow |
| Rendering model | Sequential interpreter - each mnemonic updates pen position, selected pen, or paper state before the next |
| Released | HP-GL late 1970s; HP-GL/2 1990s |
| Open standard | Yes · royalty-free |
| Specification | en.wikipedia.org |
PLT conversions
Possible
.PLT .PDFGUIDE
Yes - open the .plt in ViewCompanion or Free PLT Viewer and use its built-in PDF export, which takes under a…
How to convert
.PLT .AIGUIDE
Yes, PLT can be converted to AI - open the file in Adobe Illustrator directly or route it through SVG via…
How to convert
.PLT .DWGGUIDE
Yes -- the most direct route is ViewCompanion: export the PLT to DXF, then open that DXF in AutoCAD and save…
How to convert
.PLT .SVGGUIDE
Yes - open the PLT in Inkscape (free) and export as SVG, or upload to Convertio.
How to convert
.PLT .DXFGUIDE
Yes - use ViewCompanion to export a PLT file directly to DXF in a few clicks.
How to convert
.PLT .JPGGUIDE
Yes, PLT converts to JPG - the fastest route is opening the file in Free PLT Viewer (free) and using its…
How to convert
.PLT .CDRGUIDE
Yes, conversion is possible - open the PLT file in CorelDRAW via File > Import and save as CDR.
How to convert
Not possible
Community Q&A
asked by usersNo questions yet - be the first to ask about PLT files.
Frequently asked questions
How do I open a PLT file?
If it's an HP-GL plot, use a free HPGL/PLT viewer (Free PLT Viewer, ViewCompanion) or Inkscape, or an online PLT converter. If it came from AutoCAD it may be PostScript/PCL instead - check the file's first lines to know which viewer to use.
What program creates PLT files?
CAD and design software 'plots to file' - AutoCAD, MicroStation and similar - usually via an HP-GL/2 plotter driver. Sign/vinyl and laser-cutting software also output HP-GL .plt as cut files.
How do I convert a PLT to PDF?
Open it in an HPGL viewer like ViewCompanion or Free PLT Viewer and export to PDF, or use an online PLT-to-PDF converter. This is the easiest way to view/print a plot on a normal printer.
Can I convert a PLT back to DWG or DXF?
Partly. A .plt is just plot output, so you recover geometry (lines/arcs) but not the original drawing's layers and objects. Convert to DXF with ViewCompanion, then open/save as DWG in AutoCAD.
Why does my PLT file look like gibberish in a text editor?
HP-GL is short two-letter commands (IN; SP; PU; PD; PA...). If instead you see '%!PS' or printer codes, the .plt is actually PostScript or PCL from a print driver - open it with a PostScript/PDF tool, not an HPGL viewer.
Is a PLT file the same as a vector cut file for my plotter/cutter?
Often yes - vinyl and laser cutters read HP-GL, and many cut files are saved as .plt. Send it straight to the machine's software if it accepts HPGL.
References
1Wikipedia - HP-GLen.wikipedia.org
2Software Companions - HPGL and PLT file format explainedwww.softwarecompanions.com
