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Transparency and PDF version numbers
There is a lot of confusion in the market about how to deal with PDF version 1.3 versus 1.4 (corresponding to Acrobat 4 and 5). Some people refuse to accept PDF 1.4, hoping to avoid transparency, introduced in PDF 1.4. While this is pointless, it does cause complications in the workflow.
For example, after making a small change to a PDF file using Acrobat 5, the file is automatically “upgraded” to PDF 1.4 – even if no transparency was inserted at all.
PDF files containing transparency cause problems in many production workflows, because quite some RIPs and prepress tools are not (yet) equipped to correctly deal with its complications. Worst case, transparency may go undetected and cause the printed page to differ from the screen preview or even the hard copy proof.
The following incorrect ideas seem to be forming in some people’s minds:
· We should accept only PDF 1.3 (and not PDF 1.4) to avoid transparency · Acrobat 5 is bad because any small change upgrades the file to PDF 1.4 (e.g. adding an annotation or removing a page) · PitStop is bad because it changes PDF files, and if used with Acrobat 5, it upgrades those files to PDF 1.4 (note that PitStop Server 2.0 uses Acrobat 5 technology) · Certified PDF is bad because the file is changed at each step in the workflow to store preflight status and history log information, causing an upgrade to PDF 1.4
The PDF version number is meaningless as a way to detect transparency (or other PDF 1.4 features). For example, it is extremely easy, with standard Adobe products, to make a PDF 1.3 file that contains transparency (see next section). Consequently, the only way to make sure that a file does not contain any unwanted PDF 1.4 features is to put it through a full preflight pass, using a tool such as the Enfocus PDF Profile.
Nobody does it
To our knowledge, none of the major PDF consumers (workflow systems, RIPs, etc.) actually rejects a file based on its PDF version. We checked this with our OEM customers and on a number of mailing lists.
However, many preflight applications (including ours) can be configured to check for the PDF version number. Consequently, specific workflows may indeed reject PDF 1.4 files, mostly because their owners cling to incorrect believes, in spite of the above arguments. In these cases, Enfocus Certified PDF technology offers an excellent solution.
Using recent software versions, an Enfocus Certified PDF file retains its initial version number as long as it remains Certified. This remains true even after the file is modified in Acrobat 5 (with PitStop or otherwise). Since Acrobat Distiller 5 can produce PDF 1.3 files, this enables a guaranteed PDF 1.3 workflow using Acrobat 5 (or Acrobat 4, regardless). Simply configure a PDF Profile to reject PDF 1.4 and any unwanted features such as transparency. Then, Instant PDF, PitStop Professional and PitStop Server will do the rest – as long as the PDF file remains Certified.
Nowadays it is also possible to flatten the transparency in a PDF. This means that the objects in a PDF file are adjusted in such a way that they visually look the same, however don't contain any transparency anymore.
If you wish to do this in an automated way, then you can setup Transparency Flattening in PitStop Server starting from version 10.
PitStop Pro does not contain any transparency flattening since this functionality is already available in Acrobat itself. You can do this via "Flattener Preview" in the Print Production Tools section.
Creating a PDF 1.3 file with transparency To create a PDF 1.3 file with transparency, it suffices to open and “Save As” a PDF 1.4 file containing transparency with Acrobat 4. Only standard Adobe products are used, and no errors are reported during the process.
A similar effect is obtained when pages from a PDF 1.4 file are inserted into a pre-existing PDF 1.3 file using Acrobat 4. This produces an even more confusing result, because the “Creator” field in the resulting file is inherited from the original PDF 1.3 file. For example, one can easily produce a PDF 1.3 file with transparency, “created” by Distiller 4. In any case, the resulting file is a PDF 1.3 file that displays and prints differently, depending on whether one uses Acrobat 4 or Acrobat 5. For example, the enclosed illustration displays the same PDF 1.3 file using those two viewers, with strikingly different results.
This example PDF file has been created as follows: Using Adobe Illustrator 9:
· Step 1: Draw a yellow rectangle · Step 2: Type red text over it · Step 3: Select the text · Step 4: Add a drop shadow (Effect -> Stylize -> Drop Shadow) · Step 5: Repeat steps 1-4 to create a second rectangle with text · Step 6: Select the second rectangle and the second text · Step 7: Flatten transparency (Object -> Flatten Transparency) · Step 8: Type some more red text · Step 9: Draw a yellow rectangle over the red text (so the text becomes invisible) · Step 10: Select the rectangle and make it transparent: Multiply & opacity = 100% · Save this document as Transparency.ai · Export this document to Transparency.pdf (Acrobat 5 compatible)
Using Adobe Acrobat 4: · Open Transparency.pdf · “Save As” to Transparency13.pdf
· Avoiding transparency in PDF is an important issue (at least today), because transparency is a major headache for many RIPs and pre-press workflows. · One cannot avoid transparency by simply checking the PDF 1.4 version number, since users can easily (and unknowingly) introduce transparency in a PDF 1.3 document. · The only way to avoid transparency is using good preflight tools, such as the Enfocus PDF Profile. As an added benefit, the PDF Profile checks for many other important quality issues as well. · If PDF 1.3 would still be a requirement, Enfocus Certified PDF guarantees that the version number remains PDF 1.3 even after modifications are made to the file. In addition, Certified PDF ensures that those changes won’t introduce new quality issues (including but not limited to transparency).
To obtain the results described in this article, one must use product versions Instant PDF 2.0, PitStop Professional 5.0, and PitStop Server 2.0 (or later); earlier versions of our products may behave differently.