Printer spool files are temporary files created by the operating system when a document is sent to a printer. Instead of sending the document directly to the printer, the system first stores the print job in a spool file.
These files contain the exact printer commands that were sent to the printer driver, including text, graphics, and barcode data. Administrators, developers and support engineers sometimes need to inspect these files to troubleshoot printing problems.
Printer spool files can be inspected using a dedicated spool file viewer such as O&K Printer Viewer. It can decode printer data streams and display the printed pages visually.
What is a printer spool file?
A spool file is a temporary file used by the print spooler service while a document waits to be processed by the printer.
On Windows systems these files are typically stored in the directory:
C:\Windows\System32\spool\PRINTERS\
The spool directory usually contains two types of files:
- .SPL — the main spool file containing printer commands
- .SHD — a shadow file containing metadata about the print job
These files are normally deleted automatically after printing is completed, but administrators may copy them for troubleshooting purposes.
Why inspect printer spool files?
Printer spool files can be useful when diagnosing printing problems or analyzing printed documents.
Common scenarios include:
- debugging printing issues
- investigating incorrect printed output
- analyzing printer driver behavior
- recovering printed documents
- auditing printing activity
Because spool files contain raw printer data, they usually cannot be opened using standard document viewers.
Common printer languages found in spool files
The content of a spool file depends on the printer driver and printer model used. Many spool files contain printer languages that describe how the page should be printed.
O&K Printer Viewer can decode and display many common printer data formats, including:
- PCL5
- HP-GL/2
- PCL6 (PCL XL)
- PostScript
- GDI printing (ZjStream) – used by many HP host-based printers. To view images of printed documents you may need to enable additional registry settings. See our guide: Viewing the images of documents printed on HP GDI printers .
- EMF spooled files
- Samsung Printer Language Color
- XQX printer language
- Xerox GDI printing
- CPCA – Canon Common Peripheral Controlling Architecture
- HBPL – Dell, Epson and Fuji-Xerox printer language
- TSC Printer Language (TSPL) used by barcode label printers
These printer languages are generated by different printer drivers depending on the manufacturer and model of the printer.
Viewing spool files with a spool file viewer
Opening spool files in a text editor usually shows unreadable data because the files contain printer commands rather than document text.
A spool file viewer interprets these commands and reconstructs the printed pages.
O&K Printer Viewer allows users to open spool files and view the printed document page by page.
Instead of raw printer instructions, the viewer displays the actual rendered pages that were sent to the printer.
Exporting spool files to PDF or images
Once a spool file is opened, the decoded document can be exported to common formats such as:
- BMP
- GIF
- JPEG
- PNG
- TIFF
Exporting spool files to PDF allows administrators to archive printed documents or send them to support teams for analysis.
Understanding spool file extensions
Printer spool files may appear with several different extensions depending on the operating system and printer driver.
The most common ones include:
- .SPL – Windows spool file containing printer data
- .SHD – shadow file containing job metadata
- .PRN – raw printer output file
If you need detailed instructions for opening specific spool file types, see the following guides.
Related guides
Conclusion
Printer spool files store the exact data sent to a printer and can be extremely useful for troubleshooting printing problems or analyzing printed documents.
Although these files are not designed to be viewed directly, a spool file viewer can decode the printer commands and display the printed pages.
O&K Printer Viewer allows users to open printer spool files, inspect print jobs, and export the decoded documents to PDF or image formats for further analysis.