Each file should be a 16 million color bitmap or png image.
If you want symbols to end up grouped in a collection , make sure their names follow the rules for collections.
Each file name should be less than 28 characters. We use the Rename utility to rename any files if required.
You can create varicolor symbols by stacking a varicolor image on top of a full color one. For more information 
This is for art suitable for symbols. If you want to import tileable bitmaps as fill styles, see below.
First, make a folder under Symbols\User, with your own name, then add a folder below that with the name of the art you want to import.
If it's floorplan art, work out the the number of pixel per unit by opening the art in a paint and dividing the width in pixels by the real word width. For Dundjinni art usually the figure is 40 pixels per unit.
In CC3, on the File menu, click New. Select Symbol Catalogs, and Decide Settings Myself.
Select an appropriate blank symbol catalog.
On the Symbols menu, click Import PNG Symbols
Select the folder where the images are.
Type in the resolution you worked out in step 3 above. For overland symbols at the same scale as the ProFantasy ones, use 20. If it turns out you've got this wrong, you can always use Scale Symbols on the Symbol Manager to put it right. See below for more tips on this.
Choose the layer on which you wish the images in the symbols to appear, usually SYMBOL DEFINITION
If you want to add symbol options, tick this box and click Set. You can always change individual settings in the Symbol Manager when import is complete.
You can create lower resolution files that CC3 can use to speed up redraws. Files are: lets CC3 know what resolution the imported files are - usually Very High (full resolution) or High (if they are DundjinniDundjinni-style). Choose the folder you created in step one as the output folder.
Choose a symbol origin. For overland, it's usually center down, for floorplan, middle left.
CC3 will open another program while other resolution files are created - this process occurs; this may take some time.
When the symbols are imported, you can use Symbol Manager to reorder, rename, rescale and change symbol options.
On the File menu click Save As. Choose a location (anywhere under Symbols is fine)
In the Save as Type box, click Campaign Cartographer 3 Symbol catalog.
Type a name, click Save.
To check you are getting the symbol resolution correct when you import png symbols.
Put two or three of your symbols in a test folder (for true precision, add a png symbol of a fixed size - eg 10' wall)
Import them with your guessed resolution
Save the catalog
Start a new drawing based on an appropriate template.
Place an existing symbol of the same type from a CC2 Pro catalog, maybe a SS1 or SS2 one at a symbol scale of 1.
Place a symbol from your new catalog. They should be the same size. If not, reimport with a different scale. You can use the Distance command to find out the scale factor by measuring the heights of both symbols and working out the ratio.
It's fine to import art from multiple locations, particularly if you want different symbol options for each set of symbols.