When long pressing the empty space or text in PDF, there is a quick menu with buttons shows up. This is a cheat sheet for each icon.

Long pressing icon will also show the text of the button

Rectangle imageRectangleAdd a rectangle
Ellipse imageEllipseAdd an ellipse
Polyline imagePolylineAdd a polyline
Polygon imagePolygonAdd a polygon
Cloud imageCloudAdd a cloud
Line imageLineAdd a line
Arrow imageArrowAdd an arrow
Ruler imageRulerAdd a measurement ruler
Perimeter imagePerimeterAdd a measurement for perimeter
Area poly imagePolygon AreaAdd a measurement for polygon area
Area rect imageRectangular AreaAdd a measurement for rectangular area
Free text imageFree textType on the document
Callout imageCalloutFree text with arrows
Note imageNoteAdd a comment
Ink imageInkDraw on the document
Eraser imageEraserErase ink stroke
Signature imageSignatureAdd a signature
Stamp imageImage stampAdd an image stamp
Rubber stamp imageRubber stampAdd a rubber stamp
Search imageSearchSearch text on internet
Free highlighter imageFree highlighterHighlight anything
Highlight imageHighlightHighlight text
Underline imageUnderlineUnderline text
Squiggly imageSquigglyAdd a squiggly annotation
Strikeout imageStrikeoutStrike out text
Sound imageSoundAdd a sound annotation
File attachment imageFile attachmentAdd a file attachment annotation
Text field imageText fieldAdd a text form field widget
Signature field imageSignature fieldAdd a signature form field widget
Checkbox field imageCheckbox fieldAdd a checkbox form field widget
Radio button field imageRadio button fieldAdd a radio button form field widget
List box field imageList box fieldAdd a list box form field widget
Combo box field imageCombo box fieldAdd a combo box form field widget
Spacing text imageSpacing textAdd a free text with variable character spacing
Date text imageDate textAdd a free text with date
Group select imageGroup selectSelects multiple annotations
Lasso select imageLasso group selectSelects multiple annotations with lasso tool
Pan imagePanDefault pan tool