I recommended this App back in Nov ’14: http://www.theultralighthiker.com/gps-phone-apps-25k-vicmaps/ Many folks have probably noticed that their Pdf Maps App has updated to Avenza and that now they are only able to open three maps for free instead of an unlimited number of maps, and that Avenza would like them to pay over $30 per year to restore the functionality they had before!
As I understand it, Pdf Maps (version 1.7.3) is free software – indeed it seems that its functionality may well have been created by someone else ie TerraGo – see this Wikipedia article: https://en.wikipedia.org/wiki/Geospatial_PDF. In any case you can download it for free from a variety of sources, eg http://pdf-maps.en.uptodown.com/android/download or https://allfreeapk.com/avenza-maps,407396/
You simply uninstall the Avenza App and install the Pdf Maps App which you have downloaded. (I have downloaded a copy from the first of these and Norton declares it virus free). Then make sure you have unchecked ‘Update’. This is in the top right hand corner before you install.
This Youtube https://www.youtube.com/watch?v=fMFQupwDNhU&spfreload=10 (and others https://www.youtube.com/watch?v=IdkWwT8YKNg) tells you how to uninstall Avenza and put Pdf Maps in its place. Again, you have to be sure to cancel the ‘Update’ function so this doesn’t happen to you again.
Once again you will be able to open an unlimited number of Pdf maps for free – such as can be bought from: http://services.land.vic.gov.au/maps/imf/search/Topo30Front.jsp some of which you may need to walk The Upper Yarra Track, for example: http://finnsheep.com/THE%20UPPER%20YARRA%20WALKING%20TRACK.htm