Is it to simply resize the PDF size, to covert all text to outlines and resize in A0 size or duplicate the Indesign file and increase all the text size manually?
Technically, you could try to scale this up, even without converting text to outlines.
In InDesign, select absolutely everything via CTRL+A, then simply mouse-drag from one corner of the selection to scale up.
The trick is to hold CTRL, SHIFT and ALT (all 3 keys pressed) while mouse dragging. This will auto adjust everything proportionally, including font size, leading, stroke weight, etc. Pretty much everything scaled proportionally.
Some adjustments may be needed depending on your artwork, but generally this should work.
Scaling everything at once holding Ctrl/Cmd + Shift (not Alt!) while dragging with the mouse (as @Lucian suggested) can be quite tricky. The outer bounds of your selection is often irregular and having bleeds further complicates the operation.
A trick to do it more precisely:
- Select all with Ctrl/Cmd+A.
- Group everything with Ctrl/Cmd+G.
- Cut the group with Ctrl/Cmd+X.
- Draw a rectangle which snaps to your document bounds.
- Paste the group into the rectangle with Ctrl/Cmd+Alt+V.
- Change the document size using either Page Tool or File > Document Setup.
- Scale the rectangle to the new document size while holding Ctrl/Cmd+Shift.
- Select the content of the rectangle (the group with all the content). Either click the circular symbol in the middle or select the rectangle and press Esc.
- Cut the content with Ctrl/Cmd+X.
- Delete the rectangle.
- Paste in place with Ctrl/Cmd+Alt+Shift+V.
- Ungroup with Ctrl/Cmd+Shift+G.
To scale stroke weights and effects like this, you need to make sure that Edit > Preferences > General > Object Editing > When Scaling is either set to Apply to Content with tick marks in Include Stroke Weight and Include Effects or set to Adjust Scaling Percentage.