You should embed the fonts you use in to the document to ensure a consistent appearance. Best results are usually obtained by using the PDF or postscript format because they typically do include font information. If you embed your fonts in to your Word document, it will also work well.
Image formats, such as PNG or JPG, do not contain text data and almost always require scaling, so the text will not look its best. TIFF files must be have a width of 1728 and a 1bpp image (monochrome).