How to make a P2M file from a jpg or other pic file

From the help section of SolidWorks, only works if you have PhotoWorks

Custom Appearances

You can modify predefined appearances and save them in the custom folder of the appearance Library.

You can use Pack  and Go when you send models with appearances, decals, scenes, or  lighting, or you can select Save  appearance in the Color/Image tab of the Appearances PropertyManager.

To save modified appearances:

1. In the Appearances PropertyManager,  select the Color/Image tab and apply the properties.

2. Select any of the other tabs to apply the appropriate properties.

3. From the Color/Image tab, click Save  Appearance.

4. In the Save As dialog box:

• For Save in, accept the last folder visited or  browse to an existing folder. Typical location is: <install_dir>\data\PhotoWorks\custom.

• Type a name for  File name. Options for File Locations allow use of different  appearances with the same name.

• Select Appearance Files (*.p2m) or All Files (*.*) for Save as type.

5. Click Save.

   The file is saved and a new appearance is added to  the Task Pane. Custom appearances display a blue folder.

Additional Custom Appearance Tasks

• Delete a custom appearances folder.  Right-click a custom folder in the Task Pane and select Delete to delete from the Task Pane and  disk.

• Delete an appearance.  Right-click an appearance in a custom folder and select Delete to delete. This deletes the  appearance from disk.

As Chris pointed out, you'll need PhotoWorks to do this--that file extension is used/created by PhotoWorks to display the material's properties.