问题
I have two versions of one same scanned PDF. One of them has an OCR layer. How can I transfer the layer to the other one? I already install Ghostscript, but I don't know what to do next.
How to Use Ghostscript
回答1:
There's no such thing as an 'OCR layer' in PDF.
Most likely what you have is a PDF file which has a scanned image and the text extracted from that image using OCR which has been drawn as 'invisible' text (text rendering mode 3).
In general you can't copy and paste text between PDF files, so its very hard to do what you are asking. I don't know of any tools which will help you here, I can say for certain that Ghostscript absolutely will not help you at all.
Most likely you will also need to copy the Font (or CIDFont) from the PDF file as well, and if it has a ToUnicode CMap you'll definitely also want that or search won't work (and there's little point in this sort of OCR otherwise).
Since you have a PDF file which includes the OCR'ed text, why not simply use that PDF ? I can't see any reason why you would want to 'transfer' it to another PDF file.
来源：https://stackoverflow.com/questions/61061606/how-to-transfer-ocr-text-from-one-pdf-to-another-pdf