Safari downloads corrupted

When I download files from websites (generally by clicking on a download link) the resultant file, saved to downloads, appears to be corrupted: it shows the download progress bar as incomplete, the file type is indicated as "Safari download" rather than "Adobe document" etc, and the file has the extension ".pdf.download". I am unable to edit the name of the file to correct the extension as clicking on the filename has no effect. The issue is occurring on both my iMac and my Macbook Pro, both of which are running Safari version 9.1 on Mac OSX 10.9.5. If I edit the preferences to "Open downloaded file the file does open and can be saved from within the application (such as Adobe Acrobat), even though the downloaded version remains corrupted. "I've noticed this issue in the last couple of weeks but I am not sure if it relates to a software update.