Each semester when I am reviewing student work (and at many other times when someone sends me a PDF attachment), I am reminded that I should really put together a blog post about properly working with PDFs. There are just so many common and often small mistakes that people do especially when creating PDFs, many of which are very easy to remedy with a little care. Well, here is that document. Feel free to use it as a checklist and a reminder whenever you work with PDFs.
How to Create PDFs
PDFs from Files
First of all: It is not necessary to own Adobe Acrobat to be able to create PDFs. Many apps already have this ability built in. For example, in Word you can simply go to File > Save As… and select PDF from the option of file formats to which you can save. This process also preserves many document properties such as author credit, headings/bookmarks, and – of course – formatting. In the Save As… dialog, look for an Options button that lets you specify many settings for the exported document.
You can even use a Word file to combine different items before exporting (which removes the need to combine PDF files, more on that later). Just set up a useful paper size (letter, A4,…) and orientation and – if needed – reduce the margins to zero. Then you can can add images, screen shots etc. and even arrange them as needed before saving everything as one PDF file.
Similar functionality is provided in many other software applications as well. Where it isn’t, however, you will need to install a separate PDF creation tool. Of those, Adobe Acrobat is likely the best known, but it is not free (only the Reader version is). Other options are: CutePDF, PrimoPDF, and many others (including online services).
All of those tools install a “printer” on your computer, which you then use to create the PDF files. It is just as easy as that: Select this printer, print as you normally would and your PDF file is done. The main things to keep in mind during this process are:
- Pick the correct paper size. These tools typically default to your regional size (e.g. letter or A4) and you need to manually change that to avoid scaling.
- Do you need a certain scale in the final printout (e.g. for building plans)? Then you will want to print at a “100%” or “1:1” scale instead of selecting “Scale to fit” (or similar). Look for the scaling option when you create your PDFs – otherwise you may not be able to control this.
- Choose optimization wisely, especially for images. I’ll cover that in the next section.
- Embed fonts if the app lets you. That way, text looks the same on every computer. Make sure you don’t create the PDF “as an image” unless you absolutely want that. Images typically create much bigger PDF files than plain text.
PDFs From Scans
Sometimes you need to create PDFs from scans. For example, I don’t like to receive handwritten homework as an image (JPG). Those are very cumbersome to work with, especially if the first thing I need to do is rotate them upright. To fix this, you will need a scanning solution.
You could use a flatbed scanner if you have one. Those often come with the ability to scan to PDF, but often require you to do that from within some software (e.g. Photoshop, Word, or Acrobat). These days, phone cameras are very good and phone scanning is widely available, so why not use that. Good examples are the built-in scan tool in Google Drive‘s or MS Office‘s app, the CamScanner app, and many others.
The images below illustrate the process for Google Drive: Just click on the plus button in the app, pick the Scan option (see left image), and snap a picture of the document. You can even adjust the cropping afterwards (see right image) and change it from color to grayscale as needed.
There are a few things to keep in mind here, though:
- Flatten the paper as much as possible. Pull it over a table’s edge (on both sides), if needed. You don’t want to have edges curling up.
- Lay the page on a contrasting (typically dark) background, so that the auto-crop function gives you a better result.
- Have an even light on the page that does not create any shadows on it. Often, laying the paper in the shade (rather than full sunlight) is much better for the result.
- Hold the camera as parallel to the paper’s surface as possible. The crop tool can usually correct some distortion, but too much will affect text quality.
- Hold the camera steady while it scans. Also, make sure the scan is “upright”, otherwise you will need to rotate it in a PDF editor.
Any of these approaches will leave you with a good quality (even multi-page) PDF document that may already be quite optimized, has required fonts built in, and will at least have sufficient overall quality. For added security, some of these tools even let you add a document password.
How to Keep Size in Mind, Especially with Images
Yes, my art and architecture friends, I am especially looking at you here! Portfolio files don’t have to be huge (but they often are)! The problem with size is that with the very common high-resolution images nowadays (e.g. a 10MB 24 Megapixel image directly from the phone), it is quite common that people will simply insert many full-size images into a document. Even if they are reduced in (visible) size within the document, the full size image is often still in there.
Sometimes this is warranted, especially where a full-resolution print version is needed, e.g. for a poster or a brochure. However, emailing said brochure around for text review usually does not require full image resolution. Likewise, a large-format poster does indeed require a higher resolution so that images print well. However, there really is no joy in receiving a 50 MB attachment for an email that is to be viewed on a small screen.
Understanding DPI
The secret of success here is to understand DPI. When a document gets printed, the minimum resolution that is useful in most cases is around 300 DPI (600 DPI for extra crisp images). This means that every inch in a printout has 300 “pixels” or dots. In practical terms, an image that appears at a size of 4 inches x 6 inches on a document only needs to have a resolution of 1200 x 1800 pixels (i.e. 2 Megapixels). Any higher resolution only adds to the file size. And since JPG (and similar) images are already compressed, their full individual file size typically gets added to the document file size when it is being inserted.
Image size for a raster file format like JPG can also be controlled with a quality setting. Lower quality settings result in images that become more blotchy, grainy, and lose detail, however. Therefore, choose the quality wisely and only go with the highest setting if you really need it. Also, vector image formats like EPS can be added to a PDF at very high (lossless) quality and at a minimum cost to the file size. Consider using these where possible (mostly for line art like charts, drawings, etc.).
Depending on which PDF creator app you have, you may be able to control this fully. My Adobe Acrobat converter has various presets of which “Smallest File Size” compresses images the most. It actually reduces color images to 150 DPI and greyscale images to 300 DPI, which significantly reduces the file size but does lead to blurry images.
One option shown above is “Rely on system fonts only”. I would argue for un-checking this option because although font information adds to the size of the PDF file, it is not much and without those fonts, the document’s appearance will be different.
Again, keep in mind what kind of resolution is minimally usable. Don’t compress pictures too much if you rely on those. It is impossible to increase quality once you have reduced it.
If your PDF editing software supports it, then you may even be able to reduce the size of a PDF file even after creating it. In Acrobat, you can do this with File > Save as Other… > Optimized PDF (or Reduced Size PDF). This tool can optimize various settings, but the biggest impact usually comes from optimizing images.
If you still need to create high-resolution PDFs, consider creating two files: First, create the highest resolution file that you need. Then create a second one at the lowest resolution that is still usable. That way, you can send the second file around for printing drafts, grading, commenting etc. and have the first one for the final, high-resolution print job.
How can You Merge Multiple PDFs
This is another pet-peeve of mine: If I ask for a ten-page architectural sheet set, then that doesn’t mean that I want each page in a separate file! But… if you followed the instructions above, you would just have been able to create PDFs, but not merge pages together. What is great about the PDF file format, however, is the fact that you can put various page sizes and pages from different document sources together into the same PDF file.
You will need a rather full-fledged PDF editor for this task, though. There are several online tools available, but you often have much more control over the result (and will likely lessen the chance of catching a virus) if you use a PDF editor. Many free PDF writers will offer the ability to merge them as a “freemium” upgrade.
If you have Adobe Acrobat, there are different ways to merge files. The easiest ones are shown below: You can highlight several files and then choose the “Combine PDFs” tool from the right-click menu, or you can open one PDF, show the thumbnails bar (at the left edge of the screen), and then drag files or individual pages from another PDF into a specific location in the first file.
Afterwards, simply save the combined file and maybe optimize its size (as described earlier).
How do You Work with Comments in PDFs
I often use PDFs for reviewing files. Whether it’s grading or reviewing a draft document, PDFs are useful for a) checking the final appearance, and b) commenting during a review cycle. Depending on your PDF reader/editor software (see some suggestions above for those), you may have access to commenting by adding sticky (“post-it”) notes, text highlighting, drawing markup, revision clouds, and more. Most times, however, you will simply work with the default sticky note comment that is illustrated below:
This comment can get placed anywhere and text can be added in the flyout. Really simple!
Reviewing Comments
Where it gets a bit tricky, however, is when you need to review these comments. E.g. you may be on the receiving end of one of my graded papers. At that point, you need to make sure you see every single comment. And depending on the nature of the comment that may not be immediately obvious. For example, it is possible to highlight text and add a comment to that (e.g. for the revised text). It is not clear to the viewer then that there is anything beyond the highlighted text. And even the little sticky note icons (shown above) can be quite easy to miss on a colorful page.
To make sure you see every single comment, open the comments panel. This is located on the right side of the screen in Adobe Reader but is also available in other PDF viewers. You will, however, usually not be able to see a separate “comments” screen when you just open a PDF in a browser window. Therefore, it is usually better to download a PDF and view it locally.
The image on the right shows the comments panel with two comments. As you can see, this allows you to sequentially look through every single comment (i.e. you are not missing anything anymore). You can also use this process to add your own replies to comments which you can then send back to the original commenter.
In Conclusion
This post addresses most of the common problems that I see frequently. Of course, there is much more you can do with PDFs, such as adding text and signatures, forms, 3D, or editing the PDF itself. PDF is also widely used for construction estimating and coordination. You can read more about these tools on Adobe’s site and elsewhere, but by following my recommendations above, you are already well on your way to using PDF correctly.