The majority of our users probably aren’t aware there are some big differences between performing a Save and Save As in PDF editing applications such as Nitro PDF Professional and Adobe Acrobat. Over the years I’ve found myself referring to Save as being a ‘quick save’ and a Save As as a ‘full save’.
To talk about the difference between Save and Save As, we need to go into what are known as incremental updates. This is how the PDF References describes incremental updates:The contents of a PDF file can be updated incrementally without rewriting the entire file. Changes are appended to the end of the file, leaving its original contents intact. The main advantage to updating a file in this way (as discussed in Section 2.2.7, “Incremental Update”) is that small changes to a large document can be saved quickly.
If you haven’t worked it out already, it’s the Save operation in Nitro Pro that performs this incremental update. This is why Save always takes less time than Save As. Go on, give it a try now. Perform identical operations on the same PDF in Nitro Pro and do a Save, then compare it to the Save As.
A common thing we hear from customers is ‘after deleting content from my PDF then saving, the file size becomes larger rather than smaller!’. The reason for this is… incremental updates! If you delete something from a PDF (e.g. a page, or some text off a page) and perform an incremental update, the object you’ve deleted remains in the file, but is marked as being not used. So when a PDF viewer opens the file it knows not to display objects marked as not being used. And, because an incremental update appends information to the end of the file about what has changed, the file size increases.
Another example is if you were using the ‘Replace Image’ feature in Nitro Pro. Say you just wanted to replace a photo of yourself with a better looking version. Both are about the same file size. After replacing the image and saving the file you notice that the file size has increased more than you were expecting (because the image is approximately the same size as the original). Whilst to the eye the old image is gone, the data is still in the PDF file, but is marked as being not used (again, so the PDF viewer doesn’t display it).
- Save = faster save time, slightly larger file sizes usually.
When a Save As operation is performed, the entire PDF file is rewritten. So if you’ve deleted an image from a page, that object will not be present in the file after the Save As has completed. So in that recent example I gave, the original image that was replaced will not be included in the PDF file when it’s rewritten by Nitro Pro.
- Save As = more compact file sizes, takes a bit longer to complete.
Hopefully this has provided some insight into why the results can be different when saving files in Nitro Pro. Personally, when working on a PDF file I’ll use the Save operation until it comes time to complete the job and send the file off, at which point I’ll run a Save As to rewrite the PDF and ensure the file size is as compact as possible.
Note: There are some situations where incremental saves must be used by the PDF application, but i’ll go into that in a separate blog post.