graphicxtras.com > How to use EPS files in Photoshop as custom shapes via the creative cloud / Illustrator tutorial
Tutorial by: Andrew Buckle
Works with: Adobe Photoshop
Format: EPS / CSH
Platform: PC / MAC OS X
Other tutorials: Tutorial links
Videos: Video tutorials
The EPS artworks can be used as standard layers in PS. They can be loaded via the file open command as well as the file place command but the thing to remember is that they will then be raster artworks and not a vector. To use them as vectors is not possible other than using them as a font (the sets on this site contain the fonts and EPS format). If you use the place linked command, you can edit the content via the properties - simply click the edit contents button in the layer panel (though this does require the association to be set correctly otherwise a totally different application will open such as the preview application on the mac - you will have to use the open with command to reassociate the EPS file).
You can also use the smart objects menu command and the edit contents command (found in the layer menu) The result is opened in Illustrator and you can then copy the vector artwork back into Photoshop via the pasteboard. You don't want to copy it back as a smart object as you won't be able to define that as a CSH either, you need to select the last option 'shape layer'.
A much better approach seems to be opening the same file in Illustrator and then copying the vector into Adobe ® Photoshop ® and then selecting the shape layer option (a prompt appears during the paste of the vector material) and you will then end up with a vector layer. Still, if you go to the custom shape tool and the edit menu define command you may find the menu command is not available. To get around this, simply go to the "direct selection tool" and select the entire layer and then go to the define command found in the edit menu and the command should then be active and available and the vector can then be added to the panel and can be used in future work. This all depends on you having Adobe Illustrator and Photoshop in combo and if you are using the creative cloud / full subscription that is probably the case. Even if you don't fully appreciate all the features of AI, you can always use it simply as a tool to bring in vectors in PS
Tutorial on the subject [Youtube] The above tutorial shows the combo of PS and AI in the creative cloud.