PDF issues on opening

My computer used to be fine with opening all PDF files,however something happened no idea what.Now I can only open 50% of PDF files coming in on my Windows 7 computer.The same PDF files can be opened on my iphone so not a corruption issue .Some of them can be opened on my 7 year old Mac.I purchased PDF complete ,that was a waste of money.I have downloaded the latest acrobat .I have downloaded of this https://get2.adobe.com/reader/otherversions/ I am a total loss When i try to open certain files it says there was an error opening the file and it was damaged and cannot be repaired.If anyone can offer any advise would be greatly appreciative otherwise its off to geeks2u for is what probably a 5 minute job cheers all