A wonderful integration occurs between Reverso Context, PDF Expert on iOS. These may also be avaiable on Android. This page describes how to fully use the power of contexual lookup, which looks like this -
Highlight some Hebrew text in your iOS PDF viewer (in this case PDF Expert), and click on "Share":
Choose either of the two ways of pushing that text on your clipboard, into Reverso Context:
See the integration:
Let us say you try some words involving specially typeset charactes using a book quality PDF such as Yanshuf, a controlled vocabulary newspaper:
Notice how the terminal kaph + segol has been made into a special single Unicode character for the purpose of looking nice at the end of the line. This breaks our integration, as we're expecting to cut and paste from the pdf kaph + segol. You can see the cut and pasted text has an odd character at the end.
Never fear, with a bit of work, we can save the PDF as in image, and apply some optical character recognition to make a text layer that has regular Hebrew on it. Here is one possible way of doing this.
On Windows, open the PDF in Adobe Acrobat Reader, and print it to an image:
On The Mac, OCR it using Hebrew OCR software, such as PDF Converter OCR by Cisdem:
Then your lookup will work.
Other varations of this problem are PDF software on iOS that doesn't know about right-to-left languages, it will get the cut and pasted word the wrong way around be unable to look it up.