The upload option will only allow a single PDF file to be uploaded, however, your single file may include multiple pages. To preview your uploaded file, click on the magnifying glass on the thumbnail. You may either mail merge your own letter and envelope and upload one PDF file containing all your letters and another PDF file containing all your envelopes or send us your CSV mailing list so we can mail merge it for you. Ms Word format is NOT accepted. Typically you will do your mail merge in Ms Word and then save the results in PDF. Full bleed is not supported for this product, so please have a least a 0.25" clear margin on all 4 sides of your letters and envelopes.