Im having an issue with finiding a word in some pdf files using my ipad air2 adobe acrobat, which can be searchabe using a laptop or PC. its making me sick to do that...its says searching when i input a word in search box but never finds.. this is happning only with some pdf files, not all.
If it is happenig with some PDFs maybe you'll need to verify if these PDFs were produced from a scanning device.
If that was the case, I would run the Accessibility Checker tool with Acrobat Pro DC(in your dektop verion) and the report will indicate what exactly are the problem with that file.
I am emphasizing my inquiry about the possibility of a scanned document that was converted to a PDF because the text is rendered as an image layer on top of another image layer. Visibly on screen we are able to read what appears to be real text, but the produced PDF has no searchable text and images. Or even worse, no appropriate tagging structure (this is just a guess, I may be wrong).
You may need to run the "Scan & OCR" tool on those files to manually and attempt to have Acrobat perform a an OCR text recognition (make text and images searcheable). Additionally also try the "Print Production" tool --->>> "Preflight"--->>>"PDF Fixups" --->>> "Analyze & Fix".