Have you scanned your document with your scanner from a book and converted to pdf with a program? If so, you've got a searchable PDF but consider it's possible your PDF is just an image of the text which is why you can't select individual words.
If you have not already OCR your scanned document, try to follow these simple steps:
I would like contact you but i can't. I have think is because the kindle was bought in amazon.co.uk
it doesn't matter where they're bought - they're all identical except for the 3G models for Japan.
Question: for the first file, on the device where it works, did you send it to your Kindle with Convert in the subject line? And for the second Kindle, did you download the one from your account that you'd already sent through your account, or did you then send it again and possible forget the convert in the subject line? This would account for the different behavior