Annotation modules

HtkPDF gathers five complementary annotation modules that let you add interactive elements over the PDF content: highlights, notes, geometric shapes, freehand drawings and stamps. All these elements are stored as standard PDF annotations, and are therefore visible and editable by any third-party reader, until you decide to make them permanent through the Flatten module. These modules are available from the Editing category of the Dashboard.

Highlight

The Highlight tool applies a translucent colored background over selected text.

How to use it

Select text directly in the document (click and drag with the mouse);
In the sidebar, choose one of the six predefined colors: yellow, green, blue, red, purple or orange;
Click Highlight selection to confirm.

The button is disabled as long as no text is selected. You can alternate colors between successive highlights to create a visual categorisation system (for example: yellow = to check, green = approved, red = problem).

A highlight always relies on the PDF text layer: it aligns with the selected characters and stays readable. On an image PDF (a scan without OCR), no text is selectable and the tool is therefore inoperative.

Note (Sticky Note)

The Note tool adds a sticky note to the page currently being viewed. A clickable icon appears on the PDF; a double click opens it to reveal its text content.

Configuration

Content: a multi-line text area. The Add note button is disabled as long as this area is empty;
Icon type: six possible styles — Note, Comment, Key, Help, Paragraph, Insert;
Color: free selection through the macOS ColorPicker.

Click Add note to insert a note in the center of the active page. The content stays ready to be reused: chaining several similar notes only requires changing page and clicking Add again.

To move a note after creating it, click and drag it directly in the PDF view — or from any PDF reader (standard PDFKit).

Shape

The Shape tool draws fixed geometric annotations: square, circle or straight line.

Choosing the shape

Three buttons at the top of the sidebar let you choose: Square, Circle or Line.

Appearance

Stroke color: a palette of 15 standard colors;
Fill (square and circle only): a switch to choose a fill color. Off by default (hollow shape);
Thickness: stroke width, from 1 to 20 points, in steps of 0.5 pt.

Click Add shape to place the shape in the center of the current page. You can then move or resize it directly in the PDF view.

The operation can be undone through the Undo button in the sidebar (at the top, next to Redo) as long as the module has not been closed.

Freehand drawing

The Draw tool enables freehand mode: any mouse or trackpad movement held on the page produces a stroke, as on a whiteboard. Keyboard shortcut: ⌘D.

Configuration

Color: standard color palette;
Thickness: stroke width (adjustable with a slider).

Unlike the other annotation modules, which add an element after clicking Add, the Draw module stays active as long as it is open: each stroke started on the page becomes an Ink annotation as soon as the click is released.

Leaving the module disables drawing mode and restores the classic text-selection behaviour.

Tip: to erase a specific stroke, select it after turning off drawing mode (use the Delete key or the contextual menu to remove it).

Stamp

The Stamp tool applies a styled framed text, in the manner of rubber stamps — APPROVED, DRAFT, VOID, and so on.

Presets

Eight standard stamps are offered as preview buttons:

APPROVED (green);
DRAFT (red);
CONFIDENTIAL (red);
COMPLETED (blue);
VOID (black);
FINAL (green);
URGENT (orange);
COPY (grey).

Clicking a preset automatically fills the Text field and the matching color.

Customization

Text: a free field to enter your own text (or change a preset's);
Color: a standard palette of 15 colors.

The Add stamp button inserts the stamp in the center of the active page. As with the shape, you can then move it in the PDF view.

Behaviour common to every module

The five annotation tools share the following characteristics:

Insertion position: by default, elements are inserted in the center of the current page (except highlights, which follow the text selection, and drawing, which follows the stroke);
Later editing: annotations stay editable as long as the document has not been flattened. You can select them and move or resize them with the mouse;
Deletion: select the annotation then use the Delete key or the contextual menu;
Undo / Redo: the Undo and Redo buttons at the top of the sidebar let you cancel the last action without leaving the module;
History: when the module is closed through Apply, a checkpoint is added to the document History.

Annotations stay in pending changes until they are explicitly saved (⌘S).

Making annotations permanent

Any annotation can, by default, be deleted or modified by another PDF reader. To make your annotations inseparable from the document (the typical case of an external send, a public distribution or a legal filing):

First confirm all the annotations through their respective modules;
Open the Flatten module from the Editing category;
Click Flatten document to merge every annotation into the image layer of each page.

Once flattened, annotations are no longer distinct from the PDF content; they can no longer be moved, modified or deleted by a third-party editor.

Note: flattening cannot be undone once the document has been saved. Always keep a copy of the PDF before flattening if you expect to be able to come back to your annotations.

Screenshots

5 screenshots — click to enlarge