Transforms
Every print job arriving at RPM lands in a queue, and a queue is two ordered stages: its transforms run first, in the order you place them, each one handing its output to the next. Whatever comes out the end is what the queue’s actions receive. If a queue defines no transforms, the stage is skipped and the actions get the job exactly as it arrived.
There is no default transform chain you have to undo, and RPM will not reformat data you have not asked it to reformat. There is one documented exception, and it is a convenience rather than a surprise: if plain text arrives at a text print action or the PDF transform, RPM supplies a Text to Text Markup transform automatically and auto-calculates a layout to fit the data, rather than requiring you to configure one or falling back to six lines per inch. Add the transform explicitly when you want full control of the metrics.
That restraint is the point. A print stream that passes through RPM untouched is byte-for-byte what your host sent, which is what makes RPM safe to put in front of a system whose output you cannot afford to have quietly reinterpreted.
What the transforms do
There are currently 37 of them. Rather than reading the whole list, it helps to know that they fall into a handful of jobs:
Read what your host sends. SCS from an IBM host, ASA carriage control, First Character Forms Control, Computer Output Reduction, code page translation, and Unix line endings that would otherwise stair-step down the page. These take a format you did not choose and turn it into something RPM can work with.
Produce the format you need. PDF, HTML, PCL, PostScript and image formats. PCL to PDF converts print-ready HP output directly; the others build from text markup, RPM’s own intermediate format for describing a laid-out page.
Change the page. PCL resource mapping overrides tray, bin and copy count by name instead of byte code. Banners and separator pages go in front of a job. Watermarks lay an image under it.
Change the data. String and byte translation, a privacy filter that keeps the formatting while obscuring the text, and a family of small tools that insert, append, remove, limit and trim parts of the stream.
Use the job’s own data. Data extraction pulls values out of a job without altering it, and the filter transform runs a program of your choice on the data mid-stream.
That last group is the one that tends to change how people think about RPM, and it has its own page.
Six of the transforms named above need the Elite edition Elite only : PCL to PDF, PCL to PostScript and image formats, PCL resource mapping, data extraction, the filter transform and the PDF watermark. Every one is marked as such on the full list.
The full list
Every transform has its own page describing what it reads, what it writes and how to configure it. They are collected on the list of RPM transforms.
The size of that list is worth a moment. Most of it is not headline functionality — it is thirty years of customers arriving with one more requirement that was essential to their operation, and each time the answer being a transform that anyone can reuse rather than a special case built for one site. Transforms compose: the reason RPM handles a format nobody anticipated is usually that three existing transforms, in the right order, already do it.