Best image format when converting to PDF?

As you are working with images, I'd suggest avoiding MS Word (or any word processor application).
Rather, work out of an image editor. While there are many rather capable ones available with a price point around $100
I'd go with PhotoShop Elements (or, if the budget permits - something higher end).
Word processor apps & Word in particular are not particularly "image friendly" as compared to an photo/image editor application.You can use Acrobat directly to bring image files into PDF.
In Acrobat's Preferences, select the category "Convert to PDF".
Scroll through the list of supported file formats.
(BMP, Compuserve GIF, JPEG, JPEG2000, PNG, & TIFF are typical formats & are supported)
Most have an associated "Edit Settings" button.
Also, Acrobat Pro provides Preflights for custom checks and fixups.
Many of these are related to image processing.

If you are scanning images, Acrobat provides configuration options for optimization of the image as it comes into PDF.
(Compression for colot/grayscale or monochrome and Filtering (deskew, background removal, edge shadow removal, despeckle, descreen, & halo removal).While it is not something I do every day, I've found the import of high resolution digital photos into PDF with Acrobat Pro provides, on the whole, a pleasing result.
With that said, don't forget that the local machine's graphics card is important.
A good, mid-grade or better dedicated graphics card does make a difference as does "tuning" of the card's software & the monitor.Something obvious; but, worth stating - the higher the resolution, the larger the file size "footprint".
All those pixels add "weight".

Be well...

Thank you very much daka630. I very much appreciate your information.

Can you please elaborate on how to import an image into a PDF document? I thought I was fairly familiar with Adobe Acrobat, but I must have missed this feature. The only way I've been able to "import" an image is to designate an image/icon in a button.

Also, do you have a preference for the native image format (e.g., .tif, .jpg, .gif, .bmp, png, etc.) that works best in a PDF?

A quick disclaimer here - I bring my digital photos into PDF more for play / what-if as I'm still exploring possibilities (so many photos from over the years -- how to display/deploy for viewing by family & friends ).Assemble in FrameMaker and output to PDF?
Assemble in Captivate and output to SWF (for web or into PDF)?
Assemble in PhotoShop and output... ?
Assemble with Bridge and output... ?
Assemble in PowerPoint and output to Presenter?
Assemble in RoboHelp and output to a photo montage "Help System"?
&, of course, PDF Portfolios...With that said, bringing a supported image file format into PDF (aka "import") with Acrobat has a number of possible routes.
--| create PDF from file
--| From Windows Explorer, select file(s) & from context menu - convert to PDF
--| Use a Batch sequence.
--| scanned image into PDF
--| use a PDF containing an image as a background to another PDF.

So, as you can see, I'm looking at facets of PDF other than an image in a Button field or an image associated with a Stamp.

Something to be aware of re: a created PDF's "page size".
This can be configured in Acrobat Preferences.
In Preferences, select the category 'New Document'.
Three panes are present: Default Font; Default Margins; Default Page
In Default Page, "Size" can be selected from a drop-down menu.
If you need a custom size one can be created via the Adobe Printer Properties dialog.
(in Windows - visit the printer drivers listing, select Adobe Printer, go into the advanced options to add a new page size)

If the image (after final "tweaks") is to be "printed" to PDF from an application consider setting up a custom Distiller job option.
Distiller job options afford many configuration options.
There are 6 broad catagories.
General, Images, Fonts, Color, Advanced, and Standards.
Look over what is available for 'Images'.


For the various image into PDF paths you'll want to play what-if to determine what is optimal for your specific needs.
Oft times that "journey" is more rewarding than an immediate "destination" .But, back to your original question:

The source image's resolution (once all work-up/editing has been completed) is, essentially "fixed".
When the image is parked in a word processor or page layout or technical publishing application
(MS Word/WordPerfect/etc. - InDesign - FrameMaker) the question becomes "What does the application do to my image?". That impacts the input "information stream" to the convert to PDF process.
Most times, for most convert to PDF activities if the output PDF content is gobbered it is due to something happening in the source file's application.
An additional variable is what is used to create the PDF? Not all processes are, currently, up to snuff vis-a-vis ISO 32000-1 (the ISO Standard for PDF).

So, if it is just an image that is to be brought into PDF, my choice would be to use a photo editing application that is unequivocally "PDF friendly".


Be well...

Yes, you can with photoshop plug in. This converts well and keeps it clear. I even heard there coming out with a plug in that converts PDF's into vector