There are several file formats printers accept, depending upon what type of document is going to be produced. The best file format (in most cases) is a PDF.   A PDF (Portable Document Format) is a file format that has captured all the elements of a printed document as an electronic image, one that you can view, navigate, print, or forward to someone else. PDF files are created using Adobe Acrobat, Acrobat Capture, or similar products. To view and use the files, you need the free Acrobat Reader, which you can easily download. Once you've downloaded the Reader, it will start automatically whenever you want to look at a PDF file.

As the description from "Digital Dictionary" states, all elements are captured, all your fonts, images, color spaces and layout. Essentially a PDF is a "snapshot" of your document to be created EXACTLY as you see it. PDFs will not, however, help you with bleeds, so if you are designing a document that has an image or other element that go to the edges of your piece, please make sure that you extend them beyond the documents dimensions. Please see the illustration in the "layout" section for further clarification on bleeds. Even if you are submitting a PDF, it may be in you best interest to include the native file.

Native File Types—Layout programs we work with are InDesign, and Quark. A one page spread or poster can be in these programs or additionally, in Illustrator, but beware of placing large or too many photos in Illustrator. If you are using any other program, for instance Powerpoint, Word, Publisher, Pages, or a small office desktop publishing software, please provide a PDF. When submitting native files, please make sure that your layers are not flattened. This will allows us to adjust your design if necessary

Image Files— When submitting all your images, several file types are acceptable depending on your document and how you have used them.

JPG, GIF, EPS, TIFF, PNG— are all industry standards. TIFF and EPS files are used in the production of printed material, while JPG, GIF and PNG are used for images presented for viewing on a computer screen. When saving your images make sure you have the correct resolution and that images to be printed are in a CMYK color space. Too high a resolution can drastically slow down the equipment, while too low produces poor results.

Excerpts from— www.cesa8.k12.wi.us/media/digital_dictionary.htm Digital File Formats Explained and http://www.wfu.edu/~matthews/misc/graphics/formats/formats.html are excellent links for additional information, this last link includes a comparison chart of file types and how they effect images.