- For adding text overlay into a scanned PDF file (book/document):
- PDF-XChange Viewer Portable with OCR function
- For capturing text on the computer screen (region):
For PDF-XChange Viewer one might need to install language package first. (The installation folder is “PortableApps\PDF-XChangeViewerPortable\App\PDFV_Portable”).
Please note, that also IrfanView has a plugin for OCR. It is called KADMOS and is available via plugin page or here. However, for some reason the results were not good for the cases where I needed OCR.