We are going to print the file that we receive from you, and we'd like it to look exactly like the version that you loaded to our website. Sometimes our users create documents with unique fonts or other formatting, so the best way that we've found to make sure the printed version of your document looks like the digital version is to use PDF files - which is why our website only accepts PDF documents.
Many modern software versions allow for Saving to PDF or Exporting to PDF. If yours does not, you might want to check out a third-party PDF print provider, such as PrimoPDF.
Additionally, we've found that PDF's are more secure in the sense that they can't be modified as easily as say a Microsoft Word document can be.
Please make sure there are no security restrictions on your PDF files, or any electronic signatures, as these features can disallow your PDF from being uploaded to our website.