Section 1.3 in the manual describes what you're looking for:
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Pianoteq is available in three versions:
PIANOTEQ STAGE is for musicians who want to plug it in and play without tweaking the physical model. It includes standard features such as velocity curve, dynamics, action settings, EQ, tremolo, wah-wah, chorus, flanger, phaser, compressor and other effects.
PIANOTEQ STANDARD offers in addition powerful tools to tweak and adapt the physical model, as well as the positions of the microphones.
PIANOTEQ PRO goes even further. Its Note Edit feature allows those who require complete freedom in note shaping to edit the parameters note-by-note.
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Totally understand, it may be good to have separate manuals for each release - but, if I bought Stage and some years later wanted more, it's all there in the one manual (which is pretty detailed and well laid out).
The Link Gilles provided has an errant bracket and full stop at the end by mistake - this is what it was meant to point to:
Modartt Pianoteq Stage info page
If you click the button "Compare Stage/Standard/PRO" on that page, a pop-up with relevant info appears.
Maybe if you're having trouble finding that pop-up, there's the same info if you scroll down to the bottom of this link:
Pianoteq Upgrades
To save a click though, here's the gist for convenience.
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Included instrument packs (*see note 1 at bottom):
Stage = 2
Standard = 3
Pro = 4
All 3 versions have:
Includes KIViR historical instruments
VST, AU, AAX, NKS, Standalone
EQ, velocity curve, reverb unit
Preset (fxp) loading (**see note 2 at bottom)
If you have Stage and wonder what you miss, here's what Standard and Pro provide.
Standard and Pro additionally have:
Piano model tweaking
Advanced tuning
Microphones setting
Loads external reverb impulses
Pro additionally has:
Thousands of editable overtones
Note-per-note edit 3 (***see note 3 at bottom)
Supports up to 192 kHz audio (****see note 4 at bottom)
Notes:
* [1] Concerns new purchases from 2019 onward. During registration, you can choose two instrument packs with the Stage version, three with the Standard version and four with the PRO version. These instrument packs are fully working whereas remaining instrument packs are available in demo mode for your evaluation. You can purchase additional instrument packs at any time.
** [2] In PIANOTEQ Stage, preset loading is limited to parameters that are present in the interface. Presets built with PIANOTEQ PRO can be loaded in PIANOTEQ Standard without limitation.
*** [3] PIANOTEQ PRO lets you edit 30 parameters for each note on your keyboard. In PIANOTEQ Standard, you can explore this feature with the volume and the detune parameter.
**** [4] PIANOTEQ PRO offers an internal sample rate of up to 192 kHz. Up to 48 kHz in PIANOTEQ Stage and Standard.
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My recommendation is take your sweet time enjoying the product - it'll take anyone a lot of time to understand all that's baked in (and you can learn it fine yourself by exploring), even in Stage - and the upgrades are absolutely worth it, if you want the extra detail to design your own instruments or just make fine adjustments.
If you don't like to tweak things too much, but would like to fully load the FXP preset files from the Pianoteq FXP Corner, then Standard would be likely more than enough
Cheers.
Pianoteq Studio Bundle (Pro plus all instruments) - Kawai MP11 digital piano - Yamaha HS8 monitors