On the Hartsilapset forum, I was asked how I make the pattern PDFs so that the patterns print in correct size. As that information could be useful for others as well, I decided to post it here.
I am sure there are more sophisticated ways of doing this, but this method does not require any specific software, just what comes with your computer and scanner.
First, you need a standard size paper such as A4 or Letter. Basically anything your text processing software supports. I use A4. Trace your pattern on the paper with a black pen.
Draw side margins on the paper. The margin width can be anything you choose, but make sure it is not too narrow for your text processing software. I use 2 cm margins to make sure that the PDF can also be printed on Letter size paper.
When scanning the pattern, select an area from the left side margin to the right even if it means including a lot of empty space. Scan in black and white and select a high resolution. I use 600 dpi. This is because you need an oversized image that will not fit the page in 100% size. Save the scanned image to the hard drive.
Create a new document in your text processing software. Make sure that the page size in the program is the same as the size of the actual paper you used when scanning the pattern. Set the side margins to the same width as you used on the paper.
Now the page setup corresponds with the original paper. Insert the scanned image to the document. As it is oversized, its size will be automatically decreased so it will fit between the margins.
So, in this case I originally had an A4 paper with 2 cm margins and the pattern traced to it. Then I scanned the image from margin to margin. When I inserted the scanned image to an A4 page with 2 cm margins in the software, I ended up with an exact copy of the original paper.
The last stage is to print the document into a PDF file. Some software include this function, but if yours does not, you can use a free converter, such as PDF995.
If you are going to print the PDF file to a different paper size, such as A4 to Letter or vice versa, remember to check that the "Fit to page" checkbox (or something similar) is not marked. There should be no resizing of any kind during printing or you will end up with incorrect pattern size.