bit more information : starting from the SAME document template, with merge fields; I did check two different pdfs data coming from 2 different databases.
the one which is fine looks like this
-0.25 Tw -1953 -173 Td(NAME AND ADDRESS OF INSURED)Tj
-0.2 Tw 1953 0 Td(Please DO NOT USE )Tj
-0.5 Tw 0 -111 Td(The Blue House )Tj
0 Tw 0 -111 Td(King Street )Tj
0 -111 Td(West Malling )Tj
0 -111 Td(Kent )Tj
0 -111 Td(ME19 4QT)Tj
the one which does not look fine is
2 Tc -1953 -173 Td(NAME)Tj
0 Tc -4 Tw 294 0 Td( AND)Tj
1 Tw 241 0 Td( ADDRESS)Tj
-9 Tw 481 0 Td( OF)Tj
1 Tw 153 0 Td( INSURED)Tj
-1.2 Tc 0 Tw 784 0 Td(Please)Tj
0 Tc 255 0 Td( DO)Tj
1 Tw 169 0 Td( NOT)Tj
5 Tw 230 0 Td( USE)Tj
0 Tw 214 0 Td( )Tj
25 0 Td( )Tj
9.5 Tc -893 -111 Td(The)Tj
0 Tc 1 Tw 155 0 Td( Blue)Tj
-1.75 Tc -12.5 Tw 214 0 Td( House )Tj
0.33333 Tc 0 Tw -369 -111 Td(King)Tj
-1.35714 Tc -12.5 Tw 200 0 Td( Street )Tj
Notes:
NAME AND ADDRESS OF INSURED is plain text
The Blue House is a merge field in the RTF.
With my limited knowledge of the PDF format, I can see that there are splits which should not occur: so the question is what makes Wpdf split a string in several components or not ?