A PDF sewing pattern is only useful at its true size. A printer that shrinks the page by 3% turns a 100 cm garment into a 97 cm one, and you will not notice until it is sewn.
Set the print dialog
Choose "Actual size" or 100%. Turn off "Fit to page". The default in many PDF viewers is to fit, so check this every time, including after updating your software.
Measure the test square
Print the page with the test square first and measure it with a ruler. It should be exactly 5 cm on each side. If it is not, fix the print setting before printing the rest.
Join the pages
Trim or fold one edge of each page, line up the marks in the overlap, and tape. Work from the top left, one row at a time, on a flat table.
Cut with the grain
Keep the grainline arrow parallel to the fabric's selvedge. A piece cut off-grain can twist after washing.