I'am a developping a PDF VIEWER APP on Android and IOS. I took icons from material io icon to design my menu and so on, I am satisfied with theses icons. Howewer I don't have good icons to design my pdf viewer toolbar, for example text markup annotation icon, ink annotation icon, shape annotation .....
I was thinking of taking site icons like iconfinder / flaticon (Differents style icon in this case). Or buy custom icons created by an icon developers. Howewer I think that is bad for design, to have different style icons in an application, It means that I have to paid to remove the actuals icons, set in my menu for example, and order a set of icons for my entire app.
What is the best choice ?