PSD is default file format for files created in Adobe Photoshop. According to FileInfo.com, a PSD “may include image layers, adjustment layers, layer masks, annotation notes, file information, keywords, and other Photoshop-specific elements.” While you need a graphic design program like Adobe Photoshop, Corel Painter or GIMP to edit PSD files, you can open them in the Preview application included in Mac OS X. Preview gives you the option of saving files in a variety of formats, including the PDF format. Writer Bio
