What Is Best Ocr Conversion Of Pdf Free Online Secure No Catches

Hi,
I need to convert a many page pdf so that I can search on the text, as its all raster image type at the moment with text and diagrams.
I am always dubious of any online service incase they hold and benefit from what is uploaded, having just bought this pdf book (not locked) I dont want an unknown body using it. I had to buy two books not knowing of content to get what I want so wish to avoid further expense being able to search for words.
I dont want ransom ware either. No hidden catches, or limited to 20 pages etc, or watermarks.

What free online prog to use ?

Cheers
DBenz