Shraga: R’ Schachter once told me that you can make a Siyum if you only read the words and didn’t say them out loud.
Yekke2: The source for that is the Shulchan Aruch Harav in Hilchos Talmud Torah (brought down in the Kitzur Shulchan Aruch). For Torah Shebiksav you only have to read according to him. But Torah Sheba’al Peh you must both read and understand, if I recall correctly. (It is a Chiddush though. Pashtus should be that to get credit for Talmud Torah one would have to understand Torah Shebiksav as well.)