The name of the file I download is not the one I uploaded

Hello! I’m sure the question must have been asked before, but I haven’t found it. On my Omeka I have some PDF and Excel files that can be downloaded. Now, the name of the file I download is not the one I uploaded. For example, I upload a file named Libro.pdf, with a Dublin Core Title (in the file) that is Libro.pdf, but when I download it it is de043ce4d1c7bb87ad3e0401210aaed8.pdf
Why is this happening and how can I change it? This does not happen with images, which retain the original name.