I purchased Adobe Acrobat Pro 9 some years ago and this is more than sufficient for my needs. However when I download Forms from HM Government (UK) I'm told that I need an up to date "Reader".
Adobe provides this for free BUT will I have to delete my tried and trusted Pro 9?
Acrobat 9 should be able to handle such forms, although it's an ancient version, not officially compatible with any current OS.
Are you downloading the files directly, or do you use the Save As PDF command (or Print to PDF, or something like that) in your browser?