Hi Loose, didn't I read you were playing around with Windows 10 at some stage? Was this PDF on the machine you were installing Windows 10 on? If yes, then I found this on Mr Google and thought it may interest you.
https://forums.adobe.com/thread/1930519 If you know someone with a Windows 10 installation then try opening your PDF file in Edge. If it opens then try saving it as a different name and without a password.
Do you know if you have Shadow Copy enabled? If you do then you may be able to recover a previous version that hasn't has the password applied.
Finally and I am sure you have heard this before, always save a backup of your files on some storage media so you do not have just the single copy on your machine. If it is something important to me, I keep FOUR copies on different media but them I am a paranoid child of unmarried parents.
