PRN File Documentation

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Technical details

Feature	Value
Full name	Printer output file (print-to-file)
File extension	.prn
MIME type	application/octet-stream
Format type	Spooled printer data — a page-description or control stream, not a document format
Category	Page layout / printer data
Developer	None (generic; produced by printer drivers and the print spooler)
Introduced	Print-to-file dates to early PC printing (1980s)
Common contents	PostScript, HP PCL, PCL 6 (PCL-XL), Epson ESC/P, or raw raster
Open standard	Partial — PostScript and PCL are documented; a raw driver dump is device-specific
Byte order	Depends on the language inside (PostScript is text; PCL mixes text and binary)
Magic number	None fixed. PostScript starts %!PS (25 21 50 53); PCL often 1B 45 (ESC E); PJL jobs start 1B 25 2D 31 32 33 34 35 58 (ESC %-12345X)
Editable	No — layout and fonts are frozen into printer code
Related extensions	.ps, .pcl, .eps, .spl, .pdf
Also used by	Microsoft Excel “Formatted Text (Space delimited)” export — a plain-text table, unrelated to printing
Specification	Adobe PostScript Language Reference; HP PCL / PCL XL reference

What is a PRN file?

A PRN file is a captured print job: the exact byte stream a printer would have received, written to disk instead of sent down the cable. It is created when you tick “Print to file” in a print dialog, or when a driver is configured to spool to a file. Print-to-file has existed since the earliest days of PC printing in the 1980s, and the .prn name is a Windows convention rather than a defined format. There is no PRN specification, because a .prn is not one thing: its contents are whatever page-description language the driver that made it speaks.

That is the key idea. A .prn is device data, not a document. When you print normally, the application hands your page to a printer driver, the driver renders it into the printer’s command language, and the spooler streams those bytes to the hardware. Print-to-file simply intercepts that final stream and saves it. The result is meant to be re-sent to a compatible printer to reproduce the page byte-for-byte, with fonts, margins and layout already resolved. You generally cannot edit it and, for most variants, cannot view it on screen.

Which printer language is inside

Because the driver decides the encoding, the first job with any .prn is to work out what language it holds. Four possibilities cover almost every file.

Language	First bytes	What it is
PostScript	25 21 50 53 (%!PS)	Adobe’s page-description language; a full program describing the page
HP PCL	1B 45 (ESC E)	Printer Command Language; escape sequences plus raster and font data
PJL wrapper	1B 25 2D 31 32 33 34 35 58 (ESC %-12345X)	Printer Job Language prologue that selects paper/duplex/language, then hands off to PostScript or PCL
Raw / ESC/P / raster	device-specific	Epson ESC/P control codes or a pre-rendered bitmap for the exact model

Open the file in a text editor to read those first bytes. A PostScript job is human-readable text: it begins %!PS-Adobe-3.0, then a block of %% DSC (Document Structuring Convention) comments such as %%BoundingBox, %%Pages and %%Title, followed by the PostScript operators that draw the page. A PCL or raw job is mostly unreadable binary: you will see the ESC byte (0x1B) scattered through short command sequences, and long runs of compressed raster data with no readable structure.

PostScript print jobs

The PostScript variant is the friendliest, because PostScript is a complete, stack-based programming language rather than a static file. A PostScript .prn is a program that, when executed by a PostScript interpreter, paints the page. The header carries the DSC comments that let spoolers reorder or count pages without running the code; the body is a sequence of operators (moveto, lineto, show, fill) with fonts either referenced or embedded inline.

%!PS-Adobe-3.0
%%Title: invoice.pdf
%%Creator: PScript5.dll Version 5.2.2
%%BoundingBox: 0 0 612 792
%%Pages: 1
%%EndComments
...
72 720 moveto
/Helvetica findfont 12 scalefont setfont
(Total due: 149.00) show
showpage
%%EOF

Because it is a real program, a PostScript .prn can be interpreted off the printer. Ghostscript reads the PostScript and can rasterise the page to an image (gs -sDEVICE=png16m) or produce a PDF with its ps2pdf wrapper. If the job is already PostScript, it effectively is a PostScript file, and renaming .prn to .ps lets PostScript-aware tools recognise it. This is the one case where a .prn can be previewed and converted cleanly.

PCL and raw jobs

HP’s PCL is not a programming language; it is a stream of escape sequences that set state and place data. A PCL job opens with the reset ESC E, then commands such as ESC &l for page layout, ESC ( for font selection and ESC *r to start raster graphics, interleaved with the compressed bitmap rows themselves. Later HP printers speak PCL 6, also called PCL-XL, which is a compact binary protocol rather than escape-based text and is even less readable.

A PCL .prn cannot be interpreted by Ghostscript alone, which only understands PostScript and PDF. It needs a PCL interpreter: GhostPCL (ghostpdl) renders PCL and PCL-XL to an image or PDF. A truly raw job — ESC/P codes for an old Epson dot-matrix, or a raster bitmap targeted at one specific model — is the hardest case: it is tied so tightly to the device that the only reliable way to realise it is to send it to that same printer.

Sending a .prn to a printer

The reliable way to “open” a print job is to give it back to a printer that speaks the same language, ideally the same driver that created it. The bytes must reach the printer raw, with no further driver processing, or they get double-encoded and print as garbage. On Windows, copy the file in binary mode straight to a shared queue: copy /b invoice.prn \\PC\PrinterShare. On Linux and macOS, send it raw through CUPS with lpr -o raw invoice.prn. If the target printer does not understand the embedded language (a PostScript job sent to a PCL-only printer, say), it will print pages of code instead of the document.

The unrelated Excel .prn

One other file also carries this extension and confuses searches. Microsoft Excel’s “Formatted Text (Space delimited)” export writes a .prn that is plain ASCII text: a fixed-width table where columns are padded with spaces to align. That file has nothing to do with printing. It opens in any text editor or back in Excel, and you can tell it apart instantly because it is readable columns of your own data, not %!PS or a wall of escape codes. If your .prn came out of Excel, treat it as a text table, not a print job.

Frequently asked questions

Why is my PRN file full of unreadable characters?

Because it is a print job written in the printer’s own language, not a document. PCL and raw jobs are mostly binary control codes and compressed raster data, which look like garbage in a text editor. A PostScript job is the exception: it is readable text beginning %!PS.

Can I edit a PRN file?

Not in any practical sense. The layout, fonts and page geometry are already resolved into device code, so there is no editable document structure left. To change the content you go back to the original application and re-print, or re-export to a real document format.

How do I know if my PRN is PostScript or PCL?

Read the first bytes. %!PS means PostScript, which Ghostscript can preview and convert. ESC E (1B 45) or a PJL prologue means PCL, which needs GhostPCL. That single check decides which tool can handle the file.

References

• Ghostscript — PostScript/PDF interpreter (ps2pdf, rasterising)
• GhostPDL / GhostPCL — PCL and PCL-XL interpreter
• Microsoft — Sending files to a printer from the command line

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