Adobe Acrobat Pro will produce an index of pdf files that provides a very rapid search facility. Once the index file has been created, it can be read and used by anyone with the free version of Acrobat. The Great Eastern Railway Society's published magazines all contain this facility. These include the Railway & Travel Monthly Magazine, 1910 - 1922 as well as a complete run of the GER, LNER and BR(ER) house magazines for the period 1911 - 1963. You can find these all listed in the Files Emporium on the Society website:http://www.gersociety.org.uk/index.php/ ... emporium-2
These indexes are not human readable and allow only to search for a single word or phrase but, nevertheless, they work well if you wish to search for a location or locomotive number, for example. "Concepts" are a bit more difficult.
I have generated such an index for a limited number of ROs and find it very useful from a research point of view.
I would be happy to discuss this further, off-forum, if you wish.