you want to appear in your post as the link to be clicked
</a>

What a pity there's no way of editing these messages !

URLs
the last 3 lines of my 'template should be :

some text
</a>
 that I'm typing.

.pdfs
same thing missing, the last lines of the 'templlate' should be

‘`you want to appear in your post as the link to be clicked
`

Thanks for the tip about the backtick ! I hope this works now. . .

From below the comment box here:
"You can also put code in between backtick ( ` ) characters."

Here are the results, for anyone in the same situation :

- - -

General, applies to both images and documents :

These are the image formats you can use : .jpg, .jpeg, .png, .gif
These are the document formats you can use : .pdf, .doc, .ppt, .pptx, odt

Ensure that the item you plan to upload has a title that is usable by WordPress (letters, numbers, -) , and keep to that title. You could change the title of the item in your Media Library by editing , but it will retain the original URL. The URL cannot be edited.
For example, suppose I upload a document instrs.pdf. I then use Edit in the Media Library to change the document title to newinstrs.pdf. The UR: will continue to end with instrs.pdf. So if I write code asking for newinstrs.pdf to be downloaded, it will get a 'file not found' error.

Upload the image or document to your Media Library.
Edit its title to add the format suffix if need be, e.g. dress.jpg

The first time I uploaded images I had to wait 25 hours until they were useable, but I haven't had problems since.

The numbers in the UR are the year and month the item was uploaded,
You can see the full URL of the image or document file if you click on Edit for the item in your Media Library.

The URL in the Media Library and in the html code must be exactly the same, all lower case. I've learned the bard way that it's best to copy the URL from the Media Library !

- - -

Images :

To add an image to your post, use this html code where you want the image to appear :

<img src=”
URL of image
alt=”
text to replace image
” />

Note space before alt, and before slash.

I keep my template in this format, as it's easy to paste the replacements. But you must return it to a single line before use or it won't work.
For example :
<img src=”http://yourblogname.wordpress.com/files/2009/08/image.jpg alt=”image” />

- - -

URLs :

This is some text that I'm typing ['some text' should be underlined !]

gets coded, using the URL of WordPress as an example, as :

This is
<a href="
http://wordpress.com
/">
some text

that I'm typing.

Again straighten out the template when you've done the pasting or it won't work (retain the space after <a).

If your link doesn't work, try removing the slash from /">.

- - -

Downloadable .pdfs and other documents :

The html code for a clickable download link to a document is like the code for a URL :

<a href="
the URL of the document to be downloaded
">
what you want to appear in your post as the link to be clicked

Here are some possibilities :

instrs.pdf

Download PDF

­ right click here and "save as"

To embed the link in text , for example :
Here is a printable version of the instructions. ['printable version' underlined]

gets coded as :

Here is a printable version of the instructions.

- - -

Enjoy, if you need it this could save you hours even days of experimentation, disappointment, frustration. . . !