You are unable to upload your proposal documents to a Project because the upload slot is configured to only allow a specific file format.
For most pieces of Requested Information the file type required to be uploaded is set up by the Project Owner. In some cases, the Project Owner will request that a file be uploaded in a specific type (only .PDF, only .doc/.docx). Other times, a Project Owner may allow any filetype.
Any filetype is defined in Bonfire as the following types:
csv, pdf, xls, xlsx, ppt, pptx, bmp, gif, jpeg, jpg, jpe, png, tiff, tif, txt, text, rtf, doc, docx, dot, dotx, word, dwg, dwf, dxf, mp3, wav, avi, mov, mp4, mpeg, wmv, zip
In order to successfully upload your proposal to the Bonfire Portal, you will need to provide the file in the requested format. You can often convert the files using tools on your computer, but you may need to make this change manually.