Hammer-ons and pull-offs involve performers tapping or plucking the strings of fretted instruments with their left hand strongly enough that the corresponding pitch sounds without additional striking, producing a legato effect. Ligados are a combination of at least one hammer-on and one pull-off in a single phrase.
Hammer-ons and pull-offs are notated as the letters H or P, respectively, combined with a slur spanning the corresponding notes. Dorico Pro automatically centers hammer-on/pull-off indications on slurs. For ligados, each hammer-on/pull-off indication is centered over the range of notes in the corresponding direction. You can choose to show hammer-on/pull-off indications on each note on the Guitar Techniques page in Engraving Options.
By default, hammer-ons/pull-offs appear on both notation staves and tablature and are placed above the staff. You can change the staff-relative placement of individual hammer-on/pull-off indications. You can also hide/show guitar techniques, including hammer-ons/pull-offs, on notation staves only, tablature only, or both.
In Dorico Pro, hammer-on/pull-off indications are considered properties of notes.
- Hammer-ons
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Hammer-ons specify that the performer should tap the string at the specified pitch with their left hand without restriking the string. Hammer-ons require at least two notes on the same string with an ascending pitch direction, such as C-D. In Dorico Pro, hammer-ons appear as a letter H.
Hammer-ons on notation staff 
Hammer-ons on tablature - Pull-offs
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Pull-offs specify that the performer should pluck the string at the specified pitch with their left hand without restriking the string. Pull-offs require at least two notes on the same string with a descending pitch direction, such as D-C. In Dorico Pro, pull-offs appear as a letter P.
Pull-off on notation staff 
Pull-off on tablature - Ligados
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Ligados specify that the performer should both hammer on and pull off notes within a single phrase. Ligados require at least three notes on the same string with alternating pitch directions, such as C-D-C. In Dorico Pro, ligados comprise at least one hammer-on and pull-off.
Ligado on notation staff 
Ligado on tablature