Most, if not all pattern (*.pat) files are just renamed raster, or in some rare cases vector graphics. Try to rename the *.pat file to BMP or JPG and see if you can open it in some graphics editor. Other than that, some programs can directly import patterns and re-save them to another type of graphics.
Found 2 different conversion types using the same filename extensions.
Conversion pat to bmp type 1:
Convert from CorelDRAW vector pattern file to Standard Windows bitmap image.
Microsoft Windows software - convert pat to bmp on Windows
A set of applications used by professional graphic designers
File type (from-> to)
Convert from pat file format
CorelDRAW vector pattern file
Standard Windows bitmap image
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned pat to bmp. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Conversion pat to bmp type 2:
Convert from Gimp pattern file to Standard Windows bitmap image.
Multiplatform software - convert pat to bmp on any platform
Cross-platform batch image transcoder compatible with 500 picture image formats