May I suggest to port DocFetcher to ARM CPUs so it could run on eg. Synology and QNAP NAS devices. There could be a daemon that updates the index regularly or on changes in the filesytem.
This would allow to run DocFetcher 24x7 in a kind of a sent-and-forget-mode. PDFs and other docs are copied by the user to the network share hosted on the NAS.
When searching, the user could either use a web interface (when available) or launch DocFetcher App from that network share. Indexes would be up to date then.