The problem

Yes, you can post any article as a PDF file, if you like. An easy way is to write a very short message with the same or a suitable title and a very short body text, such as, "Please see the PDF file" or, "Please click on the attachment". Then you would attach the PDF file.

However, unless some document is available only in PDF format, posting an article as PDF only is not the best way, for a whole lot of reasons.

1. When the user goes to that message, he doesn't see anything at first and has to do a second click. Some users won't take the time.
2. PDF files are often relatively big, which can be a problem at least for users with a slow Internet connection, such as modem users. When they click on the attachment, they see nothing before the file opens in Adobe Reader. A normal web page opens instantly on the first click and show its first page of text, with the pictures coming in later for users with a slow Internet connections.
3. Some more web visitors will at that point back off and not read the file.
4. Every PDF file breaks the site navigation, because the user gets a page without any navigation elements. The only way for the user to stay on the web site is to use the back button and go back to a page he has already seen. This is not conducive to continuing to explore the web site, so PDF files have an effect like automatic ejection seats.
5. The PDF text is not picked up by the search system, so people can't search for a word combination on our web site and find the article.
6. Adobe Reader is notoriously big, awkward, and buggy.
7. Many users have obsolete versions of Adobe PDF Viewer or Adobe Reader installed that choke on newer PDF files.
8. Quite a few users don't have it installed at all and cannot read PDF files.

The solution

Post the article as a normal web page.

If there is any good reason to post the PDF file as well, for example as a print template for users, do that too and attach the PDF file to the article. It is good to give the user the choice.

Pictures

The downside is that, if there are images in the PDF file and you want to have those in a normal article too, you have to get the pictures and put them into the article. If you don't have the pictures as separate files, i.e. if you only have the PDF file, you have to use screen capture to get the pictures as separate files.

1. You can use the Images command to insert the pictures, which is very easy to do, but would put the image thumbnails on top, rather than embedding them into the text.
2. You can properly embed the images into the text, but that is more work, because you'd have to resize the images and write some HTML code to embed them. With some more work again you could create larger versions of the images that pop up when the user clicks on the embedded ones.

I believe though, that even version 1 (the Images command) is still better than the PDF, particularly since you can attach the PDF file as well, if you already have it. Version 1 has the added advantage that the abbreviated teaser, if the article is put on the front page, already shows the first few image thumbnails and will thus be more attractive for potential readers.

Theoretically there is even the possibility of doing both, i.e. combining versions 1 and 2, uploading the images through the "Images" command, yielding the clickable thumbnails and the image gallery, and additionally embedding the thumbnails or differently sized images into the text. (The "Images" command reveals the server paths and file names of the picture files, which you can then use in the HTML code to embed the pictures.) This may look a bit overloaded with each picture showing up twice (once at the top, once embedded in the text), but it does offer all functions at once.

Take your pick.