The sheet configuration is a (mainly old-style) way to define how imposed sheets should look. Sheet configurations are saved on disk (as part of the pdfToolbox library system) as files with the extension ".sheetconfig". In JavaScript imposition configurations, the sheet configuration can be (and in most cases will be) empty, as sheet definitions and slots are typically defined as part of the JavaScript runlist.

Normally, when a sheet is created in the imposition process, it is a blank (empty) sheet. However, the imposition engine also supports the use of sheet templates. These are PDF files that serve as a background. They allow creating PDF files with all relevant color bars and other marks, and use those as backdrop for imposed files. To select such a template, use the sheet configuration editor.

The runlist defines the logic of an imposition. In an old-style configuration, the runlist defines which sheets are created, and which content is placed in what slots, based on the definitions in the sheet configuration. In JavaScript configurations, the runlist typically defines the sheet definitions, slots, sheets and content placement (while the sheet configuration is empty). Runlists are saved on disk (as part of the pdfToolbox library system) as files with the extension ".runlist".

The imposition process ingests an input PDF file, and outputs an imposed PDF file. This imposed PDF file consists of pages that are also referred to as imposed sheets. How these sheets look is determined by a sheet definition. The sheet definition determines what the width and height of the imposed sheet is going to be, and which slots are placed on it.

This implies that, if you want to have an imposition configuration that creates at least two different imposed sheet sizes, there have to be at least two sheet definitions. Each sheet definition has a unique ID that can be used to reference it.

The imposition process ingests an input PDF file, and outputs an imposed PDF file. This imposed PDF file consists of pages that are also referred to as imposed sheets. A sheet can be empty, or it can have content (such as pages from the input PDF file, or decorations) on it.

An imposed PDF can have as many pages as necessary. Each sheet is created by referring to a sheet definition.

A slot is a rectangular area on a sheet. It is defined by the offset of its lower left corner to the lower left corner of the mediabox of the sheet it is placed on, and its width and height. The slot also defines bleed properties, scaling, rotation, placement, cropmarks... In a slot, it is possible to place either a page from the input PDF file, or text. The content that is placed into the slot always picks up the relevant properties of the slot (an example of an irrelevant property would be the bleed settings for text placed in a slot). Each slot has a unique ID that can be used to reference it.

A sheet definition can contain as many slots as necessary. Slots do not have to be used (filled) for every sheet. It is perfectly okay to have a sheet definition with 10 slots defined and only use two or three to create a particular sheet. Each sheet created from that sheet definition can also use different slots.

Slots are typically clipped to their size + any specified bleed, but can also be configured to be clipped at the slot boundary (without bleed). Slots can overlap on the output sheet if necessary.

While slots can contain only pages from the input PDF file, and text, the imposition configuration also allows specifying decorations. These can appear anywhere on the imposed sheet (they are defined with their own parameters, independent from the slot system. Decorations include things such as: multi-line text, barcodes, lines, rectangles, circles...

Slots include a bleed definition for all four of their sides. If a slot defines bleed, that amount of bleed from the input PDF file is used when a page is placed in the slot. Specifying bleed for a slot does not create bleed, it allows that specific amount of bleed to be visible.

As shingling is a bigger topic, it is described in full in a separate article.

Slots include two scaling factors: one for horizontal scaling (referred to as "scale x" or "horizontal"), and one for vertical scaling (referred to as  "scale y" or "vertical"). By default, slots scale to 100% of true size. Other percentage values can be used: examples would be 25, to scale down 4 times, or 200 to scale up 2 times.

Special values are 0, which signifies "scale to fit in the slot, if necessary unproportionally", and -1 which signifies "scale to fit in the slot, but proportionally.

Before being placed in a slot, pages can be rotated. Rotation is always counter-clockwise, and allowed values are 0 (for no rotation, 90, 180 and 270 (careful, -90 is not allowed, use 270 instead).

Sometimes, the content placed in a slot is not exactly the same size as the size of the slot itself. in that case, the placement property of the slot determines how content is placed. In all cases, a reference point of the content is placed exactly on the corresponding reference point of the slot. The following values are allowed:

Slots contain cropmark properties for the four corners of the slot. For each of these corners, it is possible to get all of the cropmark styles defined below.