QUESTION: What is the difference between PDF merging and PDF stamping?
ANSWER: The terms "PDF merging" and "PDF stamping" both
refer to the process of adding text or graphics to an
existing PDF file. Adding text or graphics to a PDF file
is done for a variety of reasons, including:
- Putting page numbers on the pages of a document.
- Producing variable-data documents
by adding variable text or graphics; the goal here is to
create documents that are customized or personalized in some way.
- Adding a word such as "DEMO,"
"DRAFT," or "CONFIDENTIAL" to each
page in a PDF file.
Adding such text to a document is referred to as
watermarking. The text is usually rendered
in very large letters, as solid text in a very
light color or as outline text, and it is often
oriented diagonally on each page.
Although the terms "PDF merging" and "PDF stamping"
are sometimes used
interchangeably, the PDF-publishing community usually distinguishes
between them as follows:
Depending on the goal and desired result of the merging or stamping
process, the original PDF file is altered (that is, the new text/graphics
are added to it, and it is saved under the same filename) or, conversely,
the original PDF file remains intact, and a new version of
the PDF file is created (it contains the text and graphics
from the original file plus the text and graphics that were
added during the merging or stamping process, and it is
saved under a different filename).
The term PDF merging usually refers to a process that populates
the form fields on a PDF form with
text and/or graphics and leaves intact the PDF code that
is responsible for the "live" operation of the form field.
That is: after the merging operation is complete, the form
fields that were in the original PDF file still behave as form
fields if you open the final PDF file in an application that
allows you to interact with PDF forms (such as Adobe Acrobat). Another
term for this is PDF form filling.
The term PDF stamping always refers to a process that adds text or
graphics to an existing PDF document. However the addition of the text or
graphics might or might not be accomplished by populating
fields on a PDF form. (Programmers have other
ways to add text and graphics to a PDF file.)
The key thing to know about PDF stamping
vs. PDF merging is that when you're doing
PDF stamping, if the text/graphics were
incorporated into the PDF file by
populating form fields, the form-field code
is removed from the PDF file during
the stamping operation, leaving behind only the text
or graphic that was inserted into the form field. That is: if you open the final PDF
file in an application such as Adobe Acrobat that lets you
interact with PDF form fields, you will not be able to
interact with the areas of the document where form fields
exist in the original PDF form (the one that was used as
a template during the stamping process). In other words,
after the stamping process is finished, the text and graphics
that were added to the original document are just like
any other "regular" text and graphics in the final document.
Form flattening is the term that's used
to refer to the process of removing form-field code
from a PDF file after a form field has been populated
with text or graphics.
Why is form flattening important?
The issue is that if you are creating new PDF files by using
software to add text or
graphics to existing PDF files, your final
documents could be altered quite easily by someone that
is using software that is readily available in many environments
(for example, Adobe Acrobat) if the final documents contain form fields.*
That is a good thing if
you are creating PDF documents
that are supposed to be altered after they are created — but
if you are creating PDF documents that not supposed to be altered,
it is not good if they contain form fields. Here are examples
of both kinds of situations.
Let's say that you're developing an automated
system that generates
forms in PDF format by using software that populates a PDF form
from a database (name, address, phone number, etc.). The
goal is to make it easy for potential mortgage customers to
apply for a mortgage by filling in most of the information
on the form and then
making the form available to the potential customers
in electronic format so that they can use software such as
Adobe Acrobat to
read the information on it, change any information that's
incorrect (e.g., perhaps they have a new phone number), and
add information that is missing.
In this situation, it makes sense to do PDF merging, not
PDF stamping, because you want to have form fields in
the PDF file that you create
so that potential customers can fill in the required information.
- Now let's say that you work for a company
that publishes college textbooks, and the company maintains its
electronic inventory of textbooks in PDF format. You
are developing an automated
system that can generate a new version of an existing textbook
by putting a watermark on each page. The
watermark says "EVALUATION," and the idea is that
college professors can obtain from your company a PDF file
that contains a watermarked version of a textbook for
the purpose of evaluating the contents of the textbook
to decide whether or not to buy many copies
of that textbook for an upcoming semester. You apply the
watermark to the PDF file because you
want to discourage dishonest college administrators or
dishonest professors from using the PDF file to print their
own textbooks without paying anything to your company.
In this situation, you do not want to make it easy to
remove the watermark from the pages of the textbook —
and it will be very easy to remove the watermark if
the watermark is contained in a form field. It is a simple matter
of opening the PDF file in Adobe Acrobat, clicking on the form
field that contains the word "EVALUATION," and
deleting the text.
So you'd want to do PDF stamping, not PDF merging, in this
How do you do PDF merging and stamping?
If you are a programmer, you could download the
from the Adobe Web site, read it, and write your own software
PDF merging or PDF stamping — but if you did that, you'd
be doing it the hard way! There are quite a few commercial software
products that allow you to do PDF merging and PDF stamping. Some
of them are Adobe Acrobat plug-ins
that allow a user that is not a programmer to do
PDF merging or PDF stamping interactively, by using Adobe Acrobat
on the desktop;
others are developer's toolkits or libraries that
make it easy for programmers to create an automated, hands-off
production workflow that runs in a server environment
and does PDF merging and/or PDF stamping.
To find out about software that lets you do PDF merging and
PDF stamping, click here.