I have a file with several layers and text on each of them.
Different fonts too.

How do i mass convert all text into paths without having to do it manually for every individual text ?

I'd try:

Select one text object
Menu: Edit>Select Same>Object Type
Menu: Path>Object to path

Right.
Kind of obvious too.

I use to convert text into paths with a single Union, which would merge all text in a single action.

Totally forgot about the simple convert to path command. But then i still have grouped letters.....

Raspi wrote:...But then i still have grouped letters.....

After conversion to path they are still all selected, so they can be ungrouped en-masse with one action.

tylerdurden wrote:After conversion to path they are still all selected, so they can be ungrouped en-masse with one action.

Yes, but then i would have to go to every layer, collect my individual letters and Unite them, which is what i want to avoid.

I was hoping there is a way to somehow select all text on all layers and convert them into non-grouped single word paths in one go, without accidentally joining them into one big giant path.

No, there's no 'per group union' functionality in Inkscape. I'd have needed that, too, every time I made that tag cloud for our posters...

Why not use PDF as output format with checked option: Convert text to paths ?

Cheers
P.

One more idea:
To keep each text item separate, try the following (faster than manual selection, at least):

1. Click on text, right-click, select same 'Object type'.
2. Open Object > Selection sets, click on the + icon
3. Click on the + icon right next to your new selection set name (all texts are now in the selection set)
4. Click on first text in the selection set item list, do Ctrl+Shift+C, Ctrl+U, then Ctrl++
5. Hit down arrow on keyboard, repeat Ctrl+Shift+C, Ctrl+U, Ctrl++
6. Repeat 5 until done.